Mine was bugged as I picked up both the Left and Right Eye of the Falmer, but only one could be sold to Devin (or anyone else for that matter).
He took the Left Eye just fine, but wouldn't buy the Right Eye. So I figured that maybe the Special Thieving Item was only for the Left, so I went elsewhere to sell the Right Eye. The problem is that when I went to a different vendor to sell the Right Eye, it wouldn't even appear in my inventory. This told me that my game viewed the Right Eye as a Quest Item, so I tried to drop it in a random location. No dice. I then tried to store it in a chest at Breezehome, and it told me "Quest Items cannot be removed from Inventory", so I figured that maybe it was a glitch with Devin when I tried to sell it earlier. I went back to Devin Mallory and tried to sell it to him again, and he still wouldn't take it...
So now I have a gem in my possession that is worth 5000 gold, and nothing I can do with it. I can't even use it as a creative paperweight.
Oh well, it isn't really affecting game-play at all, so I'll wait for a fix when Bethesda fixes the Quest Glitches in one of their January updates. Just thought I'd list it here so people would know.