Comment 2 for bug 839189

To add to the above, and especially given the behaviour with Trebuchet MS, where it's nice at a nice, round size of 16, and twice that 32, but fails at one point larger, I'd wager it's overzealous pixel grid snapping distorting the shape at sizes which have the tilde's waves come ever so slightly outside the grid. But I dunno how to influence that, so I can't really track down the root cause myself.