"bug" is a harsh term (to programmer's ears). If the program is operating normally at the interface, then what goes on behind the scenes, or in the file structure, may be just as planned.
Did you open the files in notepad or check the hash to see if the are the same? It could be that they are duplicates for undo functions or maybe one is a working scratch file when open in case of an abnormal exit. Anyway, unless they are growing unabated into the MB range, I would not worry about them. If it is a bug, it would be at the bottom of my list ( all else being equal).
Brew on brother!
Cheers