[PyQt] Cascade of dialog sheets broken on OSX, PyQt5.1, Qt5.02.

[lloyd konneker]

A sequence (cascade) of window modal, sheet dialogs on OSX is broken.  A 
non-working ghost of one of the dialogs is left behind.

I posted the question and demo code at 
http://qt-project.org/forums/viewthread/33684/

I am not suspecting PyQt or Qt yet, just the difficulty of working with 
OSX, or my own code.  I hope to work around it.