For some reason, from time to time, I'll have this issue where the first time I click something, nothing will happen. But, the second time I click the exact same spot, it will work as normal. This usually lasts about a day, then it goes away. It can return in a day, or in this case, after a 3-month hiatus. It is extremely annoying having to double-click everything (or tripple-click where a double-click is required). What might be causing this? It seems like the same issue described here, but I don't have jiTouch or BetterTouchTool. It is not resolved with a reboot, or even an SMC reset.