Thanks for the reply GreatMarko I completely forgot about this thread and should have checked back sooner. The problem actually occurs for files which are already on the machine. In my case both machines already had an initial snapshot of all of my songs (carried over from usb with the same folder structure and filenames). But when I turned on bitsync those songs which were already in place were suddenly renamed with the .!sync extension (not all of them, just some), unnecessarily and never renamed back