Unit stacks (tested with heroes and their offspring only so far) seem to randomly multiply... you don't notice it until you move the stack, then one unit moves, but it seems to stay too! and actually iy does... just any tile may very well (but not necessarily) have it's unit copied. If you stack them, then they appear like stacks, but until then it always looks like there is only one unit, while there can be up to four!
It does it everytime, with any heroe (custom or not) and their children. And it seems they cost money and ruin the economy 
You recognize the orginal heroe because it can't be deleted, that's how I can say the original unit moves first. You can delete heroe's copies but even though it is actually deleted, it still appears on the map, causing it to be spammed and making it hard to make the difference between real units (that keep growing ) and deleted ones 
it's a real problem when you lose many gold coins/turn and need to find the unit stack that overgrew and became overcosty amongst those already deleted and thus unclickable...
The only way to prevent it from happening seems to let the leader in garrison in a city.
debug.err : http://pastebin.com/06FtfA46
Screenshot : http://img35.imageshack.us/img35/7727/elemental1267801911.jpg
I have windows7 home premium.
EDIT : noticed copies had different names (numbers following original name) and added a few screens as examples.
RE-EDIT : it seems the bug does not happen any more when the game is launched in compatibility mode for Windows XP SP3!
