If you can't nail that pesky bug down, it helps to confess all. Go to a colleague, to your partner in health and sickness, or, at a pinch, to your cat, and tell them about the bug. You probably won't even have to finish your explanation—before you've done so, you'll have seen the light yourself.
However, even if consulting your cat does not avail you of the right solution, you might have finally stumbled onto a problem with PyQt or with Qt. In all the years that I've been developing with Python I have not come across a single bug in Python, and, what's more, I've never seen someone post a bug in Python to the comp.lang.python newsgroup.
Your first course of action should be to subscribe yourself to the PyKDE mailing list (which also has PyQt as its subject), and check in the archives at http://mats.gmd.de/mailman/listinfo/pykde, in case your problem has been mentioned before.
If it hasn't been mentioned, you might want to write the smallest possible script that reproduces the erroneous behavior. This should be easy enough if you have neatly modularized your code. You can then post this script together with the debug output (a stacktrace in technical parlance) to the PyKDE mailing list.