I had the same issue on the Raigonn encounter. (
http://www.wowhead.com/npc=56877)
There is a green bossframe showing the weakness. It does not update properly aswell. That was the first time I encountered the bug.
The bug will only appear if more that one bossframe is in place. The current bossframe you are facing will always work properly. But bossframes you are not facing (interacting with) will not update properly.
Maybe it can only be tested with other players being around doing damage to units you do not interact with. Once you swap targets the bossframe will update to the proper values. Currently it seems like the bossframes get frozen in place (receive no update) until you actively interact with them.
Maybe events are registered to player thus they will not fire if others interact?! Just guessing here sorry.