Lane swapping but you get demoted

I've been playing ranked with my friend. My friend got adc so I told him if he would like to go mid and we can switch. He agreed and we swapped. The game did end on a loss and i was still gold 1 until i was punished for lane swapping and was demoted to gold 3. I wasn't even trying to lane swap for an advantage. We were literally the same rank. I don't understand why this would be in the game. I'm a I missing something?