Wtf!

Your problem could be any number of things; you could have a piston not fully engaging during hard braking, a rotor with a heat spot in it, a pad that cocks it self a bit during braking, uneven fluid distribution due to trash in the system, and many more. Your best best would be to look at all four corners to start trying to diagnose the problem, as well as the master cylinder and proportioning valve. Just remember that most of the parts and pieces we buy now days are made over seas, and the people that make them don't care about the "foreigners who buy them". Just my 2 pennies worth.

Bill S.