Tower agro not switching

I was playing against bots as varus (blue) team in summoner rift. I'm not sure if it is an intended action or a game play bug but thought to report it.

I was attacking tower along with 2 castor (blue) minions. tower agro was on one minion. That minion was about to die and at that exact moment a teammate ( graves) tped to that minion.

Minion was immune, which I know is an intended action but tower didn't switch it's agro and i was able to take down that tower in that duration. I thought tower will switch it's agro and is an issue.

If tower is not intended to switch it's agro then it's a perfect game play to tp to dying minion and make the whole take down faster (and easier). Also without a shot, tower won't be able to ramp up it's damage.