I have tried this with two different control surfaces now, with the same result.
I have two Channel Strips assigned to the same volume fader in - in this case - a Korg NanoControl 2.
I wish to switch between them. Previously I would add a second mapping for the button, map both mappings to Mute at the Channel Strip level, and then ensure that Button On for #1 was Mute and Off was unmuted, and vice versa for #2. Button is set to an unused CC. This still works.
In the interests of CPU efficiency I decided to change the behavior from Channel Strip -> Mute to Channel Strip -> Instrument -> Bypass. When I do this, the mapping for instrument #1 is accepted but when I try to repeat this for #2, selecting Bypass in the Instrument puts the legend "PDF Page" in the mapping tab instead of "Bypass".
The instrument in question is Aruria's Mini V. I haven't yet tested with other instruments to see if it's the same.
Is anyone else seeing this or able to reproduce it? Click on the "broken" image below to see the result.