I have loaded several VST plugins created by Cabbage (2.0.03, 64 bits) in LMMS (V. 1.2.0-rc in Windows 10), combo boxes close immediately after being clicked on and therefore none of their items can be clicked (they are fully functional in Cabbage though). The same happens with the free plugin Tunefish4. Is there a workaround?
I don't think so.
It's this issue: https://github.com/LMMS/lmms/issues/3918
It's a bug in JUCE, which is software that Cabbage depends on. We may work around it on the master branch after lmms-1.2 is released. It was deemed a bit too dangerous to touch this close to a stable release.