I know you guys know this, but here's a reminder to lube, wipe down, and occasionally check all the moving parts of your trainer bike, especially if it's permanently on the trainer. Thought I was doing so, and then realized I had never checked the rear brake caliper. Cable is pretty much fused into the ferrule. I'm guessing that I was sweating on the housing, which dripped/wicked down into the cable/ferrule interface. D'oh!
I've soaked PB Blaster into it, so far nothing. I'll check it again when I get home tonight. Durr, what a pain.