#if JUCE_WIN32
if (GetThreadPriority (GetCurrentThread()) <= THREAD_PRIORITY_NORMAL)
filter->setNonRealtime (true); #endif
in juce_VstWrapper.cpp
I don’t know for what broken host it was added, but it is definitively breaking the isNonRealtime flag on Cubase 4 (the real-time audio thread gets called with a priority of -12 here)
edit: it is not cubase 4 specific, so maybe it is vista specific…