I'm pretty sure this is a graphic glitch, but if it isn't I assume some moderator will move this to the correct place.
Also I confess I didn't check if this have been posted already.
During a game I had purify +2, a Dune scorpion hit me, so he poison me with neurotoxin, then I have +1 AND neurotoxin, the yellow poison counter with +1 at the bottom left. After I cast a card the counter dissapears (its effectively 0), so I keep casting cards, and then I notice i'm being damaged each turn for a crescent ammount, while there is no visible counter of poison where it should be. It appears to me that the neurotoxin is still working if casting over a purify which I assume is intended, but if you get to 0 poison counters while still having neurotoxin the image that is supposed to announce you how much counters of poison you have dissapear.