Target spell -doesn't work?!

[BB Shockwave]

I hardly used this spell as a Paladin, but now my mage with an undead army could put this to good use with ghosts... except, it doesn't work.

No matter how I try, even low-level pirates and priests will ignore the spell and attack my other units.

What am I doing wrong? Maybe Target doesn't work on undead? I'm using the latest patch...