Bug or Feature?

[Triomega-bloodsail-buccaneers]

Oh, and to add to that, they went in more detail in this thread. This is likely the most relevant post to what you’re experiencing:

@Kaivax

The bugfix to leash behavior of groups of enemies makes the game behave like it did in original WoW. We discovered the problem because of Solenor the Slayer, but it was a bug with all linked combat groups’ leashing behavior. The fix only affects linked combat groups with a leash timer, so there are still plenty of situations when you might attract the attention of multiple enemies and be able to split one off.