Steps to reproduce:

• While in a game, the opponent needs to be at 2 or less life;

• Put into play a creature that has health 2 or less, and that has the ability 'Finale: deal 2 damage to the opponent' (for example, play a 'Cranial Consultant' followed by a 'Caller of the Cursed');

• The opponent needs to cast a 'Drain Blood' (Spell: Drain 2 from an enemy creature) on the creature and successfully kill it.

At this point, the expected course of actions is for the opponent to heal 2 life and take 2 damage at the same time, such that his life total is effectively unaltered, and the game continues.

However, what actually happens is that, although the life total of the opponent is computed correctly (and the opponent is shown being at 1 life), upon spell resolution the win animation is played (the one that starts from the character portrait and ends at the opponent character portrait), immediately followed by a similar lose animation, and finally the victory screen shows up (the one with that shows the rank/event progression and the planeswalker celebration animation). Upon exiting the match and returning to the main menu, if playing on ladder, thropies will be subtracted as if a loss had occurred.

I suspect the same thing would happen whenever an opponent would take an amount of lethal damage and heal from the damage at the same time, but I didn't do further testing beside the case explained above.