[PyQt] QGraphicsWebView -> QGLContext::makeCurrent(): Cannot make invalid context current.

[Doogster]

The attached program runs fine. However, on every machine I've tried
it on, it prints several dozen warning lines when closed:

QGLContext::makeCurrent(): Cannot make invalid context current.
QGLContext::makeCurrent(): Cannot make invalid context current.
QGLContext::makeCurrent(): Cannot make invalid context current.
...

These do not appear until the program is closed.

It happens on a Lenovo T400 with an X4500HD, running Slackware 14.0
(qt 4.8.2, pyqt 4.9.1), and also on a Macbook Pro with an NVidia
GeForce GT 330M ()

While these errors appear to be harmless, they don't look good. How do
I fix whatever is causing them to appear?
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