I just vanished a bug: for some reason the uncompression algorithm we use worked in most cases, but not in the most important part: at self-updating.
I debugged, changed, debugged, … And nothing.
Finally I found it: at 1 place in the code I used QDir’s mkdir() method instead of mkpath() and in some cases it tried to create a directory which’s parent directory was not yet created.
It took me hours to figure it out. But now, everything works perfectly, and can continue to do more productive tasks :)
So remember: use mkdir() if you know for sure the parent directory does exists and mkpath() if the parent may not yet created.