Three-Finger mouse gestures not working

My three-finger gestures — click, tap, and swipe seem to not be working. Using Live view I very occasionally see a three-finger gesture for which I have assigned a keystroke, in order to test the gesture, but most of the time it doesn't register. I have tried it with Fingers Must Be Near Each Other (Clicks tab of advanced Mouse preferences) both on and off. Nothing in my OS X Mouse preferences uses 3 fingers.

More info: This is weird. I had defined control-3-finger-click and option-3-finger-click a while ago but forgot about them. Both of those work. When I define unmodified 3-finger-click to do the same thing as control-3-finger-click, 3-finger-click does nothing.