http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/video/vesafb.c#L349
http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/arch/i386/boot/video.S

Maybe vesafb doesn't even use a "mode" at all.  See the first link.  That's
worse than I thought.  If so then fbset is returning bogus information supplied
by vesafb.c.

The answer then is vesa-tng which has improved (?) since grml's problems with
it.  Note the copyright on vesafb.c line 7, 1998, really old.