I was having the same problem today and discovered the issue is in a slightly non-current release of Apple's CoreAudioUtilityClasses, AUMIDIEffectBase class. Due to multiple inheritance the following needed to be added to AUMIDIEffectBase.h so that AUPluginDispatch calls the correct overridden methods.
virtual OSStatus MIDIEvent( UInt32 inStatus,
UInt32 inData1,
UInt32 inData2,
UInt32 inOffsetSampleFrame)
{
return AUMIDIBase::MIDIEvent (inStatus, inData1, inData2, inOffsetSampleFrame);
}
/*! @method SysEx */
virtual OSStatus SysEx( const UInt8 * inData,
UInt32 inLength)
{
return AUMIDIBase::SysEx (inData, inLength);
}
I just pulled the latest from Apple's site: https://developer.apple.com/library/mac/samplecode/CoreAudioUtilityClasses/CoreAudioUtilityClasses.zip and it looks like they already fixed the issue. We both had bad download timing, it seems!