Tea with milk in it is a abomination anyway, a complete act of sacrilege. If you are going to debase the almighty leaf suspension then who the hell cares when you defile it with bovine lactate.
You are going to ruin the tea, destroy it's subtle flavours and forever render it to be a shadow of it's former glory, the order and receptacle in which you desecrate it, be it mug, pot or even in the kettle matters not, you are still a monster.