one of Elise's spiders that someway ended up on bench

So... I have played a match in which one of Elise's spiders got somehow on bench. Tried to sell it, but surprinse! When I dragged it to sell, it shown that the spider cost 0 gold. I tried to sell it using E but I could not. It was automatically put on the board after I levelled up, so it was counted as a champion. I did not notice that until the next fight, when the health bar of that spider got red and my nidalee fought it.