Edit: This is definitely a bug, but it appears to be a display issue since relogging into the game fixed the problem. I am playing online FYI.
I put my normal exalted catalyst in my inventory and equipped The Cuckoo. I ran a monolith and the cuckoo changed to a new exalted item. All good so far. I put the cuckoo exalted into my stash, and equipped a new Cuckoo unique. My usual exalted catalyst was still in my inventory. After killing more enemies, it got weird. Instead of the Cuckoo changing into an exalted, my usual exalted catalyst changed into a duplicate copy of the exalted that the first Cuckoo had turned into. I no longer had my original catalyst, I had 2 duplicate random exalted cuckoo catalysts, and I still had a Cuckoo in my off hand.