Sorry I didn't reply sooner.
I don't know if you kept the gmbrc file and if you are still willing to help me find the issue, but if you are :
I really don't know why ctrl-c doesn't work, that's very strange, I use it all the time with gmb. You can try sending the signal with the command kill by finding the process ID, with for example "top" and doing "kill -2 PROCESS_ID", though I really don't know if this will make a difference.
I've found a way to get a full trace of the execution, download the file
http://gmusicbrowser.org/files/SimpleTrace.pm and follow the instructions at the top of the file if you want to give it a try.
Feel free to ignore this if you can't reproduce the problem anymore, and/or don't want to bother.