I have an original Radio RA system that has worked for 15 years flawlessly, except the dimmer over the sink is whacked out. Can turn on the light and it ramps up like normal then it will just start ramping down back up, down a couple clicks and back up - it's like it's controlled from somewhere else. The green LED stays lit the whole time, so it doesn't act like a loose connection or anything like that. None of the other switches act up. Have you ever seen that happen before and is it likely to be just the dimmer itself?

I unplugged the repeater from power, and in about five minutes, the dimmer's not acting goofy. But why would the repeater be talking smack to just one of 10 devices, and the others all act normal?

It's next to a sink- have you removed the switch, to inspect it? Being near water, I would bet that it was sprayed and now, the water is working its magic.