[GAMEPLAY] Tahm Kench kind of unable to eat Heimerdinger turrets

So I was playing Tahm Kench, and i was having a fun game, and then something weird happened: I devoured a sleeping turret, but instead of getting in me, it stood down back on the ground, and became invulnerable for the duration of the devour. Seemed kind of weird to me. It happened consistently throughout the game. Link is to the actual game.