Hah, I think I just found something out. If I checkout the file with cvs co -p -r 1.119, then I get the right data. However, if I use co -p1.119 (the RCS equivalent), I get the broken data.
So it seems that it all boils down to some exciting incompatibility between GNU RCS and the builtin RCS in CVS... :-P
Well, fortunately cvs2svn has a switch to use cvs to checkout stuff instread of co, so it should be simple enough to fix the problem...