I have been having a similar problem. I have been noticing that if I hit a bump while on the brakes, the ABS will kick in almost like I lose my brakes for a second, but I can feel the pulsation in the pedal. Then the brakes will "catch" and it's like I hit the brakes too hard all of a sudden. I also get the ABS and brake light from time to time, but it always resets once you turn the key off like the OP described.