I stumbled on this while testing COLORMAP generation algorithms.
Do :

  $ prboom -iwad /path/to/doom2.wad -file backwards.wad

Start MAP01 at HMP skill. Pick up the chainsaw. Meet the former
humans. You'll soon notice that they act strange. Indeed, they
will always face you, even while moving away from you. This
gives the unreal impression that they're walking *backwards*.
The imps do the same.

The COLORMAP lump in backwards.wad, apart from making corpses
shine in the dark, is too short. For some serendipitous reason,
this causes PrBoom to misbehave in this wonderful manner.

Reproducible on i386 with both the Debian 2.2.2-1 package and
version 2.2.3 compiled from source.

I'm reporting this bug under the condition that you promise NOT
to fix it. Bugs like this should be pampered and looked after,
not fixed.