Untargetable Invisible Gangplank barrels

During the last fight of the game, we got the enemy team low and I placed a barrel in the middle of them, but when I tried to shoot it using Q it had become untargetable, both of my barrels were nearly invisible and became active only after I died and the enemy destroyed them. I knew it was a bug, since the enemy had no disables, but the barrels became nearly invisible, like Fizz' "E"... Needless to say that lost us the game.