Clicking resize handle (sometimes) snaps window borders to screen edge

[Adam Conrad]

This is about 75% reproducible on my machine, and hard to put into words, so I've recorded a video. What's happening is that when I click on the resize handle, the window borders immediately snap to the right and bottom (sometimes just bottom) edges of the screen. Debugging attempts so far:

1) disabling 'grid' plugin had no effect
2) changing resize mode to 'normal' had no effect (except that, obviously, the window blows out instead of just the resize outline)
3) playing with edge attraction settings in 'snapping windows' plugin appeared to have no effect