Rygarius
Shadowmeld's (Night Elf racial) functionality received a bug fix in Patch 6.1 to address a number of issues with the ability that wound up affecting its behavior in PvP combat. A hotfix is being worked on (it's not ready yet) that will restore Shadowmeld back to the way it worked (while keeping the bug fixes intact).
Update: The hotfix to return Shadowmeld back to it's pre-6.1 functionality after tomorrow's rolling restarts should be going in later tonight.