Problem:
There currently exists a bug on Mario Kart 8 online where, depending on how a player enters or exits an online lobby before or after they vote, causes the entire lobby to disconnect after the 10 second countdown. This bug is reproducable under these situations and it is largely contributing to the instability of Mario Kart 8 online. It affects all online modes.
Symptoms:
The game will initiate the 10 second countdown despite all votes submitted.
The number of players in the lobby will not be the same amount on all player screens.
The number of votes will not be the same amount on all player screens.
Causes:
It seems to happen because the online protocol has not been programmed properly to gracefully handle the exception. The exception in this case seems to be caused by a discrepancy in how a lobby exchanges information between players and what information players are actually receiving.
If exploited properly, a person is able to disconnect rooms at will. This is a genuine concern for the online service of Mario Kart 8 and should be dealt with as soon as possible.