Detailed information is in the gcc bug tracking system, Bug #511. This prevents, among other things, KDE 2.0 from compiling, so I'm setting the priority to high. KDE 2.0 will be released in a couple of days.
I'm currently working around this bug by moving the enums out of the classes; this works, but it's crappy and not binary compatible...
Should be fixed in gcc-2.96-60 in rawhide.