Resizing QOpenGLWidget stuttering

QOpenGLWidget frequently hangs for 1-2s when rapidly resizing a window. This even occurs with empty content (trivial app attached).

This coincides with the GPU switching clock rates. This occurs with Qt 5.5.0 and Qt 5.6 beta. It does not occur with Qt 5.4.2.

There are several other bugs on various platforms about poor resizing performance which may have the same root cause.

Edit:
The problem isn't the clock switching - other applications trigger switching to higher clock rates without stutter. But 5.5.0 is clearly doing some much more expensive operations when resizing than previous versions.