FOUND THE PROBLEM.
Or at least, I narrowed it down to a particular device.

My URC KP-900 remote control is the culprit.
Went back to finish my programming today.
Noticed the KP-900 batteries were dead.
Replaced them.
About 15 minutes into a frustrating programming experience, I noticed that nothing was working again.

Sure enough, the RF LED on the sensor was lit up constant.

Thought about it a moment.
Pulled the batteries from the KP-900 and sure enough, the RF interference went away.

A minute later, I duplicated the same situation.

Gonna try a factory reset on the KP-900 to see if that helps.
It's a new-old-stock remote.