My 1999 GMC Sonoma has a occaisonal problem–the tail lights stay lit after the light switch and the ignition are turned off. The brake pedal does not appear to be sticking. The cure has been to remove both light bulbs, wait a few minutes, plug them back in, and all is well. This might happen an average of once a month, seems more common in hot weather.
I would have the brake light switch checked. It may be defective or simply out of adjustment.