With JUCE 1.50, the setSpeakerArrangement function in the VST wrapper has been changed considerably compared to 1.46. Unfortunately, when inserted on mono tracks, the demo plugin now crashes in the process() subroutine as numInChans and numOutChans are not set to one. Hence I have changed the respective lines in setSpeakerArrangement to
speakerInChans = numInChans = pluginInput->numChannels;
speakerOutChans = numOutChans = pluginOutput->numChannels;
which seems to have fixed the issue.