Vampire hypnotize can fail

[Grayshift]

The rising opinion seems to be that it's the sunglasses, but I'm not sure that's right. If something as simple as that blocked it, it surely would have been noticed far sooner. Vamps hypno sec officers with regularity, I'm sure.

So I'm not certain this is actually a bug report, or just a question: What the heck makes a vamp's primary disable fail?