A nasty bug with the 2-piece Tier 10 bonus for Elemental Shamans reared its ugly head recently when a player attempted to use Elemental Mastery. The bonus, which is supposed to reduce the cooldown on Elemental Mastery by 2 seconds each time Lightning Bolt and Chain Lightning is used, instead puts the 31-point Elemental talent on a whopping seven day cooldown. This is akin to the bug found with the Hunter ability Call Stabled Pet, which puts the ability on an even more staggering 25-day cooldown.
Ghostcrawler immediately responded to the concern as raised on the official forums, stating that the problem happens only in cross-server instances and that raiding shouldn't be affected. Elemental Shamans sporting two pieces from the Frost Witch's Regalia would probably do well not to activate Elemental Mastery while in a dungeon using the Dungeon Finder until a fix is found. Ghostcrawler stated that Blizzard is working on the issue.