diff --git a/build/linux/platform_specific_code/juce_linux_Audio.cpp b/build/linux/platform_specific_code/juce_linux_Audio.cpp
index 68991865c1..3bc69fa3fd 100644
--- a/build/linux/platform_specific_code/juce_linux_Audio.cpp
+++ b/build/linux/platform_specific_code/juce_linux_Audio.cpp
@@ -814,8 +814,7 @@ public:
         internal->setCallback (callback);
 
         if (callback != 0)
-            callback->audioDeviceAboutToStart (internal->sampleRate,
-                                               internal->bufferSize);
+            callback->audioDeviceAboutToStart (this);
 
         isStarted = (callback != 0);
     }
diff --git a/build/macosx/platform_specific_code/juce_mac_CoreAudio.cpp b/build/macosx/platform_specific_code/juce_mac_CoreAudio.cpp
index 8524fe544c..22e1190198 100644
--- a/build/macosx/platform_specific_code/juce_mac_CoreAudio.cpp
+++ b/build/macosx/platform_specific_code/juce_mac_CoreAudio.cpp
@@ -1001,8 +1001,7 @@ public:
         if (internal != 0 && ! isStarted)
         {
             if (callback != 0)
-                callback->audioDeviceAboutToStart (getCurrentSampleRate(),
-                                                   getCurrentBufferSizeSamples());
+                callback->audioDeviceAboutToStart (this);
 
             isStarted = true;
             internal->start (callback);
diff --git a/build/win32/platform_specific_code/juce_win32_ASIO.cpp b/build/win32/platform_specific_code/juce_win32_ASIO.cpp
index 891aaef72a..39d4e5ebce 100644
--- a/build/win32/platform_specific_code/juce_win32_ASIO.cpp
+++ b/build/win32/platform_specific_code/juce_win32_ASIO.cpp
@@ -763,7 +763,7 @@ public:
     {
         if (callback != 0)
         {
-            callback->audioDeviceAboutToStart (currentSampleRate, currentBlockSizeSamples);
+            callback->audioDeviceAboutToStart (this);
 
             const ScopedLock sl (callbackLock);
             currentCallback = callback;
diff --git a/build/win32/platform_specific_code/juce_win32_DirectSound.cpp b/build/win32/platform_specific_code/juce_win32_DirectSound.cpp
index ea235c9ebc..b12015104d 100644
--- a/build/win32/platform_specific_code/juce_win32_DirectSound.cpp
+++ b/build/win32/platform_specific_code/juce_win32_DirectSound.cpp
@@ -1162,7 +1162,7 @@ public:
                 return;
             }
 
-            call->audioDeviceAboutToStart (sampleRate, bufferSizeSamples);
+            call->audioDeviceAboutToStart (this);
 
             const ScopedLock sl (startStopLock);
             callback = call;
diff --git a/src/juce_appframework/audio/devices/juce_AudioDeviceManager.cpp b/src/juce_appframework/audio/devices/juce_AudioDeviceManager.cpp
index bfb92e50bb..e0fdf6d565 100644
--- a/src/juce_appframework/audio/devices/juce_AudioDeviceManager.cpp
+++ b/src/juce_appframework/audio/devices/juce_AudioDeviceManager.cpp
@@ -414,8 +414,7 @@ void AudioDeviceManager::setAudioCallback (AudioIODeviceCallback* newCallback)
                 lastCallback->audioDeviceStopped();
 
             if (newCallback != 0)
-                newCallback->audioDeviceAboutToStart (currentAudioDevice->getCurrentSampleRate(),
-                                                      currentAudioDevice->getCurrentBufferSizeSamples());
+                newCallback->audioDeviceAboutToStart (currentAudioDevice);
         }
 
         currentCallback = newCallback;
@@ -446,10 +445,13 @@ void AudioDeviceManager::audioDeviceIOCallbackInt (const float** inputChannelDat
     }
 }
 
-void AudioDeviceManager::audioDeviceAboutToStartInt (double sampleRate, int blockSize)
+void AudioDeviceManager::audioDeviceAboutToStartInt (AudioIODevice* const device)
 {
     cpuUsageMs = 0;
 
+    const double sampleRate = device->getCurrentSampleRate();
+    const int blockSize = device->getCurrentBufferSizeSamples();
+
     if (sampleRate > 0.0 && blockSize > 0)
     {
         const double msPerBlock = 1000.0 * blockSize / sampleRate;
@@ -457,7 +459,7 @@ void AudioDeviceManager::audioDeviceAboutToStartInt (double sampleRate, int bloc
     }
 
     if (currentCallback != 0)
-        currentCallback->audioDeviceAboutToStart (sampleRate, blockSize);
+        currentCallback->audioDeviceAboutToStart (device);
 
     sendChangeMessage (this);
 }
@@ -603,9 +605,9 @@ void AudioDeviceManager::CallbackHandler::audioDeviceIOCallback (const float** i
     owner->audioDeviceIOCallbackInt (inputChannelData, totalNumInputChannels, outputChannelData, totalNumOutputChannels, numSamples);
 }
 
-void AudioDeviceManager::CallbackHandler::audioDeviceAboutToStart (double sampleRate, int blockSize)
+void AudioDeviceManager::CallbackHandler::audioDeviceAboutToStart (AudioIODevice* device)
 {
-    owner->audioDeviceAboutToStartInt (sampleRate, blockSize);
+    owner->audioDeviceAboutToStartInt (device);
 }
 
 void AudioDeviceManager::CallbackHandler::audioDeviceStopped()
diff --git a/src/juce_appframework/audio/devices/juce_AudioDeviceManager.h b/src/juce_appframework/audio/devices/juce_AudioDeviceManager.h
index c8f702c9f9..0655083503 100644
--- a/src/juce_appframework/audio/devices/juce_AudioDeviceManager.h
+++ b/src/juce_appframework/audio/devices/juce_AudioDeviceManager.h
@@ -369,7 +369,7 @@ private:
                                     int totalNumOutputChannels,
                                     int numSamples);
 
-        void audioDeviceAboutToStart (double sampleRate, int blockSize);
+        void audioDeviceAboutToStart (AudioIODevice*);
 
         void audioDeviceStopped();
 
@@ -385,7 +385,7 @@ private:
                                    float** outputChannelData,
                                    int totalNumOutputChannels,
                                    int numSamples);
-    void audioDeviceAboutToStartInt (double sampleRate, int blockSize);
+    void audioDeviceAboutToStartInt (AudioIODevice* const device);
     void audioDeviceStoppedInt();
 
     void handleIncomingMidiMessageInt (MidiInput* source, const MidiMessage& message);
diff --git a/src/juce_appframework/audio/devices/juce_AudioIODevice.h b/src/juce_appframework/audio/devices/juce_AudioIODevice.h
index 5f418c1e0a..76fd51139a 100644
--- a/src/juce_appframework/audio/devices/juce_AudioIODevice.h
+++ b/src/juce_appframework/audio/devices/juce_AudioIODevice.h
@@ -35,6 +35,7 @@
 #include "../../../juce_core/text/juce_StringArray.h"
 #include "../../../juce_core/containers/juce_BitArray.h"
 #include "../../../juce_core/containers/juce_OwnedArray.h"
+class AudioIODevice;
 
 
 //==============================================================================
@@ -103,13 +104,15 @@ public:
         callback has just been added to an audio device, or after the device has been
         restarted because of a sample-rate or block-size change.
 
-        @param sampleRate           the sample rate it's going to use
-        @param numSamplesPerBlock   the intended block size - this isn't a guaranteed
-                                    figure; see the notes about numSamples in the
-                                    audioDeviceIOCallback() method.
+        You can use this opportunity to find out the sample rate and block size
+        that the device is going to use by calling the AudioIODevice::getCurrentSampleRate()
+        and AudioIODevice::getCurrentBufferSizeSamples() on the supplied pointer.
+
+        @param device       the audio IO device that will be used to drive the callback.
+                            Note that if you're going to store this this pointer, it is 
+                            only valid until the next time that audioDeviceStopped is called.
     */
-    virtual void audioDeviceAboutToStart (double sampleRate,
-                                          int numSamplesPerBlock) = 0;
+    virtual void audioDeviceAboutToStart (AudioIODevice* device) = 0;
 
     /** Called to indicate that the device has stopped.
     */
diff --git a/src/juce_appframework/audio/dsp/juce_AudioSampleBuffer.cpp b/src/juce_appframework/audio/dsp/juce_AudioSampleBuffer.cpp
index 7bfd53093b..8bc05d8420 100644
--- a/src/juce_appframework/audio/dsp/juce_AudioSampleBuffer.cpp
+++ b/src/juce_appframework/audio/dsp/juce_AudioSampleBuffer.cpp
@@ -316,7 +316,7 @@ void AudioSampleBuffer::addFrom (const int destChannel,
                                  int numSamples,
                                  const float gain) throw()
 {
-    jassert (&source != this);
+    jassert (&source != this || sourceChannel != destChannel);
     jassert (((unsigned int) destChannel) < (unsigned int) numChannels);
     jassert (destStartSample >= 0 && destStartSample + numSamples <= size);
     jassert (((unsigned int) sourceChannel) < (unsigned int) source.numChannels);
@@ -409,7 +409,7 @@ void AudioSampleBuffer::copyFrom (const int destChannel,
                                   const int sourceStartSample,
                                   int numSamples) throw()
 {
-    jassert (&source != this);
+    jassert (&source != this || sourceChannel != destChannel);
     jassert (((unsigned int) destChannel) < (unsigned int) numChannels);
     jassert (destStartSample >= 0 && destStartSample + numSamples <= size);
     jassert (((unsigned int) sourceChannel) < (unsigned int) source.numChannels);
diff --git a/src/juce_appframework/audio/midi/juce_MidiBuffer.cpp b/src/juce_appframework/audio/midi/juce_MidiBuffer.cpp
index f93fdfbf74..fad79b3314 100644
--- a/src/juce_appframework/audio/midi/juce_MidiBuffer.cpp
+++ b/src/juce_appframework/audio/midi/juce_MidiBuffer.cpp
@@ -53,9 +53,14 @@ MidiBuffer::MidiBuffer (const MidiBuffer& other) throw()
 
 const MidiBuffer& MidiBuffer::operator= (const MidiBuffer& other) throw()
 {
-    bytesUsed = other.bytesUsed;
-    ensureAllocatedSize (bytesUsed);
-    memcpy (elements, other.elements, bytesUsed);
+    if (this != &other)
+    {
+        bytesUsed = other.bytesUsed;
+        ensureAllocatedSize (bytesUsed);
+
+        if (bytesUsed > 0)
+            memcpy (elements, other.elements, bytesUsed);
+    }
 
     return *this;
 }