qsort doesn't sort arrays that are defined with double elements.
You can find attached a script that shows this function working well for int (as described in the ctypes documentation). If int array is replaced by double array qsort doesn't sort any more.
Even worse, with python 2.6, the difference between a[0] and b[0] may be nan.
The script can be launch by 
python.exe testQSort33.py