Watchpoints w / xDebug in Eclipse PDT?

Anyone got any breakpoints to work when debugging PHP with xDebug and Eclipse? As I understand it, I should be able to select the watched variable in the expression view, or select the variable in the Variables view while debugging and then select Run-> Toggle Watchpoint. But Toggle Watchpoint is constantly on. All my other debugging functions work fine: breakpoints, input, shutdown, etc. I just can't get the clock function.