JP1 Remotes

When devices are too dissimilar to share a single protocol, keymoves are the best solution without a device combiner. Your bogus OBC on mute is also a good workaround.

Extenders and some remotes have keygroup mappings / activites where you can mix devices. Not sure which remote you are using these days.

The Mute glitch is on the One-For-All URC-3680.
My wife has a Charter OCAP C4000 URC-1060BC2.
The unassigned Mute was acting like a Power key [OBC = 0] on my Aiwa stereo.
Other tested unpopulated Mute assignments had OBCs of 0 & 255. Single devices retained their device numbers. Combo devices had unrelated device numbers.

Regarding your findings with the MUTE button, all JP1 remotes have 3 button groupings where it's "all or nothing", meaning you have to populate all of the buttons in the group, those groupings are:
* the 10 number buttons
* the 3 volume buttons (including mute)
* the 2 channel buttons

When you create an upgrade using RMIR, if you populate at least 1 button in a group, you have to populate all of them, and if you don't, RMIR will assign hex code 0 to the un-populated buttons. Typically, people don't notice because they don't expect the button to do anything as they didn't program it. But if you want to guarantee that it doesn't do anything, then you can program an OBC that you know does nothing, to it, like you did.

Good to know. Thanks.