The question has been posed several times: What happens if you have master loot on an a BoP recipie drops which requires a profession the master looter does not have ? All GM answers so far have been that this wouldn't be a problem. But it seems that this is not the case.
I can confirm that this is actually true at the minute - If a master looter does not have the required profession when a BoP recipe drops, then that item will be unlootable.
We have recently implemented a fix to correct this problem, and it will be pushed out with patch 2.1.0, which will be with us Soon.
Following the thread there you will see a link to a bluepost claiming the opposite.
This is not a problem for my group, as we're running with FFA since BWL. For others, you might want to consider this until fixed.