Maybe if simply using allowable targets doesn't work then maybe you could create a buff which increases damage by x% and then just simply select all your specified targets and give them the buff when the ability is in action.
Yes, wards are wierd like that, alot of stuff doesn't work on them. What you may need to do is make all your wards units, just look and act like wards?
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.