Creating a clone of the player stops you moving.
To recreate, simply do something like "placeatpc "player",1,1,1". You will be unable to move. Your clone appears to have default inventory items (possibly default stats too); also, your clone appears to be hostile and will attack you.
Revision c5a60445
(RM-2216 from redmine: created on 2014-12-16 by Stuart Moore, , closed on 2015-03-12 by scrawl .)