QGLWidget 30 fps maximum on Windows XP

I'm trying to get a QGLWidget to swap buffers at 60 fps (the monitor refresh rate), but it seems no matter what I try, the fps maxes out at 30 fps. If I drag a corner of the window to resize the main window containing the QGLWidget, the fps jumps and starts approaching 60 fps, but as soon as I stop dragging the fps drops back down to a rock-solid 30 fps.

I've read that "window manager" may be responsible for such a low frame-rate, but I'm not sure what that means or if it's even relevant (there's so much conflicting info re: opengl out there -- so many things to try that don't work).

Does anyone know what's going on -- why is the fps seemingly locked to 30 fps?

Frustrated,
~ andy.f

Whelp, 30 fps definitely seems to be the maximum for WinXP (on my machine, anyway). I tested the qml-scenegraph qt-labs project on the same machine using Windows 7, and the fps is not limited to 30 fps like it is on XP. I guess that's what's meant by "window manager".

At least I've got a good reason to switch to Win7, now =)

Cheers,
~ andy.f