hey Rory - scott here - it's been a fair bit of time! hope all is well with you...
i fired up Cabbage and trying the various synths again and noticing that with live MIDI input notes are sticking quite a lot, even for an older serial interface spec (MIDI). it's also happening on the GUI keyboards as well, though. my 'Mac' has been updated to a macOS High Sierra and i'm on your latest release.
additionally i used a really simple demo script that came with the [csound6~] object i'm using in PD (i'm back to PD again). in PD this script works perfectly and is quite robust. i also opened this up in CsoundQt with absolutely no problems. so i think something must have changed on the MIDI input front because as it is it's pretty much unusable for me. it might be the macOS version. i just tried 2.0 and had the exact same issue of sticking notes. i'm on 10.13.6 BTW
Ian's synth demos as well as their onscreen keyboards also stick though not quite as often.
anyway any light you can shed here would be great. i'm investigating using a few of Ian's instruments in PD using [csound6~], but not finding Cabbage to be a good testing area for this. i would love to just use VST plugins in PD but it seems on macOS that having the VST GUI and the audio in the same thread (which apparently is now required) is problematic and is still an issue needing to be solved.
PS - one other weird issue - seems like a lot of user icons in the forums are now coming up broken. not sure what's up with that, but also happening in latest Firefox as well as Safari. mine's fine. i wonder if it's the automatic letter icons that aren't rendering.