Sending a bank select message to some old SynthEdit based VSTs, e.g. several of the classic GTG series by Mik Sybrandt, causes what appears to be a silent factory-bank reset; the user-selected program is displayed in the relevant dialog but the default patch is played.

This can sometimes be worked around by blocking CC messages, e.g. by inserting REAPER’s JS MIDI Note Filter plugin¹ in front of the instrument and allowing only notes to pass; FalkTX’s CARLA plugin host has similar functionality, though I don’t remember how it worked.

Adding ‘cc0=-1’ to REAPER’s Preferences|Audio|Playback: CC Reset Overrides also seems to work, but may be a bit global for some tastes.

Of course, computers being what they are these days, it may not work after all. As Mr. Scott said, the more they overtake the plumbing the easier it is to stop up the drain…

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¹ There’s also a JS MIDI CC filter available through ReaPack. Harrison Mixbus has one in the x42 plugin suite, which also has “CC2Note: Convert MIDI control change messages to note-on/off messages.” That might actually let you hear what was going wrong…