Surge-type brakes:<br />I've had my trailer just over a year. Yesterday we dumped the boat off at the lake(My trailer/boat only sees lakes, no salt water), returned home. Backed the empty trailer up into the driveway. When we went to leave an hour later, both brakes were seized. Backing up, moving forward, even with two large people sitting the trailer, wouldn't unlock the brakes. I eventually had to bleed the lines dry to retrieve the boat. <br /><br />What would cause this?