Brakes lockup on power up?

[NuclearLeaf]

Tonight when I press the brake pedal and pushed the power button, the brake pedal felt stiff, like manual brakes. The car powered up as normal, but would not move forward or reverse, the brakes were locked up. I cycled the parking brake, but it was not on and that did not help. I cycle the car on and off a couple of time, no help, still the same problem. I begin to think that this was some kind of electronic issue, so I decided to disconnect the 12 volt battery to see if that would help. When I disconnected the negative terminal, I heard a loud thunk, like a relay dropping out. The brakes released and the car rolled up against the parking pawl. I reconnected the negative terminal and powered up the car as if nothing was wrong. Drove home without any other issues. Has anyone else had a similar problem?
2012 SL with 38,000 miles.

 

[keydiver]

The only time I have felt anything similar top that is after the car sat overnight in the rain, or after I washed it, and the brake pads rusted fast to rotors. It always scares me when it snaps loose.

 

[ksnogas2112]

The only time I have felt anything similar top that is after the car sat overnight in the rain, or after I washed it, and the brake pads rusted fast to rotors. It always scares me when it snaps loose.

I've had the rust problem after rain, snow, ice, car wash.