When I set one radio to channel "A=1" and another to "B=2," a signal sent to 1 of them still shows up on the other. I thought radios had to be on the same channel to see each other.

Can you post a screenshot of your setup?

Now it's working as described in the manual.
It never fails. Dev's reply for more details, and redoing the tests, makes it work.

I'll let you know if it glitches again, and try to give more details.

If you can save the game in a bugged state, we can use Global Variable Viewer to see what went wrong. I asked for the picture just in case there was a physical wire accidentally connecting the two radios.

This whole mod is in need of a rewrite given how many other glitches there are, but I personally won't have time for it until summer.