I joined this game :

So i played it, and finished it after someone suicided.

I had 1 heart left so i decided to join another game. To my suprise my heart was gone.

I looked back and found that apparently i had made another game while being in the first one :

And it ended while still playing the other game with a suicide by my side, when i did not know i was in another game:

As you can see in the proof, i was still in the first game, when apparently i was also in the second game and vegged.

I lost 1 heart because of it :c And i suppose this is why people get -hearts.