As it is often the case, the developer forgets to try only one thing and it is always where the problem lies.
In my case, when I was off in vacation, a colleague did upgraded my Debian and somehow it messed up my default JDK. So before I was compiling with Sun's JDK, and now I am compiling with GCJ (GNU's Java implementation). Alghough I did not believed that would make any difference, I switched back to Sun's JDK. It worked.
So it seems that GWT Compiler reuses some resource-loading mechanism coded somewhere in the JDK/JRE and that GNU's Java implementation does something radically different than Sun's Java implementation when resource-loading is concerned.
Last edited by pdimitar; 11 Feb 2009 at 2:34 AM.
Reason: Forgot to specify that I had the same problem.