I think this is not a Python bug, since it concerns PyQt. 

You're passing a QString object to os.path.split(), while the official
documentation wants you pass a Python string.

However, when I tried to run your example, newWF.py, and tried to open a
file from the menu, I got this:

controls.nch: 1024                                                    
Controls Window data shape: (511, 1024)
Data file: None
/home/marco/Programmi/Python-2.6.3/pyconfig.h
Traceback (most recent call last):
  File "issue7158.py", line 277, in openDataFile
    head,tail = os.path.split(filename)
  File "/usr/lib/python2.5/posixpath.py", line 77, in split
    i = p.rfind('/') + 1
AttributeError: 'QString' object has no attribute 'rfind'

Why does this happen? 
`filename` is a QString object. (you can see why here:
http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/qfiledialog.html#getOpenFileName
)

So how do you split your filename? I don't know.

I should close this bug.