Okay, the file is actually not at-menu.ogg, but at-demo-2.ogg.
That file IS being released by the adonthell people under the terms of the GPL - the archive wastesedge-src-0.3.4.tar.gz on the adonthell website contains no note about the music tracks being licensed under another license.
If you did not grant the adonthell people the rights on the music under the GPL, they are not allowed to release it that way. They have to clearly indicate which parts are covered by the GPL and which aren't. Currently there is no such indication - the source archive just contains the GPL in the COPYING file and states in the README that the game (which means the whole game, of course, as there is nothing saying only part of it is covered) is released under the terms of the GPL.
So legally, the only ones violating your copyright seem to be the adonthell people who released the files that way - one can't blame MikeeUSA for believing what he read in the adonthell licensing terms.
HOWEVER: just taking the music without asking is rude, no matter if it is allowed or not. And IF you allowed the adonthell people to release your music under the GPL, this probably is the last time that you licensed music under that license. See what such rude people are causing.
Now... I do not know if that music has a so-called "source"... but if it has, the GPL requires anyone who distribute it to provide the source on request. For music, "source" seems to refer to either the score or the tracker input file. If it's improvisation, there is no such thing, of course - the recorded file then "is" the source and there is no problem. I am not sure if you or the adonthell people are aware of the consequence of putting music under the GPL... it basically means:
- Anyone can use the music for his own GPL project!
- Anyone has the right to receive the source (score, tracker files) of the music!
- Anyone even has the right to EDIT that source and rebuild ("re-record") it, as long as the result is still put under the GPL!
For music, you may be better off with one of the creative commons licenses - but then the music is licensed differently from the rest of the game and thus can't be provided in the same package.
1. Open Notepad
2. Paste: ÿþMSMSMS
3. Save
4. Open the file in Notepad again
You can vary the number of "MS", so you can clearly see it's MS which is causing it.