Brake assist fade

[gsobol]

I was standing in traffic and I've noticed that my car started moving forward even though that I haven't taken my foot off the brake. I've applied more pressure and the car stopped, but few seconds later started moving again. I've done a test, when you pump the brake in very small increments, NOT releasing the pedal all the way up (!) (approx 20-30 pumps), the pedal will go all the way to the floor and releasing it a millimeter will allow the car to roll forward. Releasing the pedal all the way up returns things to normal. I've owned the car over 3 years, and that's the first time I've noticed that. None of my previous cars exhibited such a behavior, although I've had brake failure on the Lincoln that was caused by a failed relay (electrical brake assist). Any suggestions, or should I take it straight to the dealer?