I have searched the forums to the best I can, and double and triple checked the patch notes and I believe they either gave a nerf to the fight or it is a bug.
As of at least last night (1/27/2012) and at least in NiM 16 Man Firebrand/Stormcaller, the shields are no longer able to be targeted. We did verify that AOE would still damage the shields but at the very least you cannot "accidentally" tab or click into them to make them your target.
Personally I like it, because it saves me time having to press tab one more time as I switch targets, but it would be nice to know if this was intentional or not.
Noticed the same thing this week when doing 16 man nim tanks.