Snowball Mark/Dash bug
If a snowball is thrown, and happens to be in range of a champion's corpse the exact moment the champion resurrects, it will mark the champion. This mark will be on the champion's now resurrected body...at the fountain. And if you dash while they are marked, it will take you ALL THE WAY to the fountain.
I've ended up doing it many many times on accident and I've seen other people do it as well.
It's very unexpected when it happens because you're not sure where the snowball marked if it's offscreen and you have the ability to dash only to end up in the enemy fountain.