Bug or Feature?

[Triomega-bloodsail-buccaneers]

I believe what you are experiencing may be related to the Hotfix on Oct 22nd:

@Kaivax

Fixed a bug that caused creatures such as Solenor the Slayer to misbehave when pursuing the player. Groups of creatures that commit to combat as a group will now all continue to pursue whenever any one of them are struck by a player attack or ability.