Phantom break failure?

Last night, I was biking home, chugging up the Rosslyn hill. Bike performing fine, after spending the cold day in the not-too-cold garage at work. At the Nash/Marriott parking lot light, I stop, using my brakes, and they work normally – specifically the lever moves a tiny amount with no effort, then gets progressively harder to squeeze. A few feet past the intersection, I go to slow a bit, tap my rear brake, and the lever basically gives me no resistance; I can squeeze it all the way to the handlebar. Huh?

This is an ebike (Yube elBoda), upgraded to BB7 disc brakes and squeezing the rear brake lever switches the Bionx system to full re-generation mode, which slows the rear wheel. That, coupled with the weight of the bike, and the fact that I was aiming uphill, meant that the bike slowed as much as I needed it to, so no immediate danger. Continuing up the hill, I verified that my front brake was working fine. On that first little downhill I verified that I could stop. So I continued home, slower and more cautious than normal. The entire time, the rear brake seemed to have failed.

This has never happened to me, but I’ve read your stories on the forum. I’m thinking maybe my cable snapped or … who knows. When I got home, I headed upstairs to greet family and warm up, and didn’t get back down to the bike until this morning. Well, this morning, the rear brake was looser than I remember, but definitely engaged, and would completely stop the wheel when fully engaged. I adjusted the bolt by the lever to make it tighter, and rode in without problem.

So, forum-nati, what do you think happened? Did my cable snap but the magically garage trolls fixed it overnight? Did the brake actually fail on the ride in the cold last night, but in a way that was fine after a night in a garage? Should I be worried about this happening again? What should I do about it?

Thanks!!!