eg.. the + str one.
you have say 2 caster champions in the army stack. get 1 to cast it on the stack and someone (not sure who gets it, haven't checked that much).. then try casting the same spell again with the same/different caster and it tells you you can't cast it. you can move one of the champs out of stack, cast it and rejoin with no problem though.
seems to have been introduced in one of the patches.
