this strange bug is not bug in mercenary code itself, it depend on StackAid problem - for all players with ID > 20 (StackAid was designed for support 20 civs), StackAid update (after place mercenary in city) failed, which lead to cancel merc placement code -> merc unit is not deleted from wait pool -> is placed again in next few turns -> error in stack aid, not deleted from pool -> and again and again....
quick solve:
edit StackAid.py (Total Realism/Assets/Python/ directory )
at lines 44-48, there is something like
aScout = [0,0,...,0]
.
.
aSiege = [0,0,...,0]
each array must contain at least twenty-five 0 (zeros) - 24 for max civ, 25th for barbarian
then you can delete cloned merc - maybe some merc will arrive again (because is in pool), but after that it will be removed from pool correctly and not cloned in future
Mexico
EDIT: in TR world map, player with ID > 20 (which is affected with this bug) is:
Mehmed II
Ragnar
Shaka
Brennus
and another note: somewhere in Warlords bug thread was mentioned Mehmed II bug, which can lead in CTD for some graphics cards (when meet Mehmet) - if you are affected, read this:
http://forums.civfanatics.com/showthread.php?t=181960
(this will be included in next patch from Firaxis)