Yeah, once a MIDI channel is assigned NNA handling assumes that a plugin is assigned, and since the NNA of this instrument is set to "Continue", we have to assume that the NNA channels are essentially playing indefinitely (because you might want to cut those notes on NNA channels at a specific point in time using S7x). As no plugin is assigned in this particular case, the MIDI-specific code should probably not be running. And when a plugin is assigned, we probably need a smarter voice stealing algorithm to avoid running into the same situation.

Fixed in r22595. The problem can still occur if the instrument is associated with a VST plugin (even if it's not an instrument plugin) or the MIDI I/O plugin if a valid MIDI channel is assigned and NNA=continue is chosen. I will reduce the impact of that a bit by allowing such NNA-ed channels to eventually be taken over based on how long they have been playing but that change will probably not be backported to 1.31 like r22595 was.

More fixes in r22602 for channels associated with MIDI-capable plugin types and NNA=continue.