You mean you want the target you polymorph to still be able to fight? In the object editor for the spell, you can try changing what the target gets morphed into, so instead of a sheep, into a orc grunt, or maybe edit the sheep unit so that it can fight. Just an idea, don't know if it works.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.