I've seen this type of thing happen many times before...and can only offer this advice:

If it's not a 100% guild run, always clarify the loot rules before you start the raid. Be specific - tell them what spec you are playing and if you can role on that particular spec's loot if it drops.

This way if they ninja the gear you can report them, as blizzard now considers these types of actions scamming.

Source:
http://forums.worldofwarcraft.com/th...No=9&sid=1#165

Hope this helps...

Cheers,
S.