Incorrect damage display amounts
I was attacking with several creatures which represented lethal damage, but during the damage step but before damage was actually dealt in the animation my opponent conceded. This resulted in their life total being displayed as 0 when they conceded, but still taking damage from my creatures and their life total being represented at a negative amount much lower than it should have been (-7 rather than 0). This has no actual impact on the result of the match as far as I can tell, but it may be confusing for people who don't realize what happened and could cause problems and misunderstandings. Definitely not high priority, but something that the devs should be aware of.