Ai using Custom Heroes

[Drazhar]

I'm unsure of how to get the Ai's to use custom heroes, however both teams are undead, and I only want one type of hero for each team, not the same. I've been able to make the computers make the hero type they're meant to, by changing the death knight and the dreadlord into my custom heroes, and then removing the other 2 from the altar of darkness and then limiting both teams to one type of hero each, but only one seems to make one, the other team won't, they'll just collect resources and advance no further, and after testing it a few times it seems whichever team makes their hero first is the only one to keep advancing, the other won't.

Thanks in advance