If you create a QPixmap("filename.png") object, the contents of filename.png are added to the internal QPixmapCache of the QPixmap class. If later on in the same existence of that object, the loadFromData() function is used, the original "data" is not detach()'ed and the internal QPixmapCache copy is now polluted with whatever was loaded in manually.

The documentation of detach() mentions that all write operations should automatically detach from the QPixmapCache, but in this case it isn't happening.