Is it 100% of the time only certain slaves work from certain windows? If you spam cast from one window do the others never do anything? Do you get error messages?

If you swap the spell name on just the ones that fail to work to, say, Wrath, do they work?

Try putting a /say or /emote in the macros so you can see if they're even registering as being clicked.
Once i saw that the spells were not working correctly, I hearthed back to TB and started to trouble shoot by attacking the Alliance dummies on the Hunter's Rise. As far as I can tell it happesn 100% of the time. I kept retesting it on my own many time before posting here.

I will try throwing another spell in that spot and tossing some /say commands in there too and see if I can find out more on whats going on.