Currently on the PTR, the Nothing Personal trait for Assassination Rogues fails to apply if Vendetta is cast and another ability is immediately queued up. The entire trait fails to apply (both the energy buff and dot).
You can replicate this by just using Vendetta and spamming Garrote or Mutilate before the cast goes off.
This macro will replicate the issue every time:
Vendetta will be cast and the Garrote cast will fail because of the global cooldown. As a result, Nothing Personal does not proc, but Vendetta will be on the target.
Edit: Okay, the trait just appears to be broken in general and isn’t caused by this behavior in particular. Nothing Personal just fails to apply in most cases no matter what you do. Guess I just got some convenient luck while testing.