Not sure if this is a bug, but it happened to me.
I was using Mp3tag to edit some files on an external drive connected via USB.
Later, I invoked Mp3Tag again, but this time the external drive was not connected. The program just hung.. presumeably looking for the last set of files it had loaded from the external drive, which of course was not connected anymore. There was nothing I could do to interrupt it, stop it, cancel it, except use CTL+ALT+DEL to kill the process.
The only way I could get MP3Tag running again, was to reconnect the external drive again.
I am using v2.37d with windows XP Pro.