I got an Elise spidering on my bench and couldnt get rid of it

As hilarious as this was, it eventualy got anoying as it cost me a roster spot. Not sure exactly how this happened but I was upgrading an Elise at the same time as many other units. I was actually able to put it on the board and it would fight as a normal unit and put swap it between the board and bench. when i tried to sell it for 0 gold then it just remained on the slot on my bench until the end of the game