Show Power is part of the same area in the Editor that Show Range is located.
It's irrelavent to your problem however, and after comparing the Siege Tank and Photon Cannon I couldn't locate anything that's a dead giveaway. I also took a look at the Sensor Tower, and again nothing is jumping out at me.
I have a feeling that there might be something in the Events+ of the actor, but I'll look into it tomorrow if someone else hasn't fixed your problem by then.
Good night, sorry I couldn't help you more.