(Cata) PvP gear bonuses work?

Hello everyone,

As you may or may not know, some people use 2 different sets in PvP (e.g. Balance/Resto set, Elemental/Resto set) to get 2 times the 2 set bonus of 400 resilience (so you get 800 resilience). I've heard by someone that this is only a visual bug and doesn't really add any resilience to your stats (even if it shows +800 in your stats window) so I would like to know by a moderator or a GM if the 2 set bonus works fine or not and if it's intended or not.

Thank you for you time.