Mark of the Bleeding Hollow not proccing?

[llamalaugh]

Hi there!
I have a question for any rogues using 2x mastery enchants (bleeding hollow) on their weapons.

Against player targets, should the bleeding hollow enchant stack when entering combat? when attacking a raiders training dummy/npc It seems I can get both of my weapons to proc the bleeding hollow enchant (well, most of the time anyway...).
But when attacking players/player training dummies it never seems to stack on the opener, rarely even procs one of the weapons?

Was this some kind of fix to limit burst damage in pvp? or am experiencing a bug?