Mid-battle in the Kobold wagon adventure, I hovered over the cards in my Elf character's inventory. They highlighted my Elf on the board, making it bounce up and down as normal. After a few bounces, the Elf disappeared and became a black circle, which I assume is an underlying art asset. The character remained a black circle for 1-2 more turns, then returned to "normal" at the start of another turn. (In my 20 hours of play, this is the only occurrence I've seen and it otherwise didn't impact game play.)
Just saw this again, very briefly, in room LZRD. 1. My dwarf fighter played a Walk card 2. The Lizardman net took effect, overlaying his Walk 3. Either just before or just after the card effects rose from the bottom of the screen, a black circle replaced the fighter's bouncing character icon 4. The black disc was visible for perhaps 2 seconds before the regular fighter icon returned It appears to be a graphic update (a black image mask?) that's slowed down mid-stream, probably by browser processing. (Here's a capture of the room number and situation. Reduced image size to allow upload for the post.)
Took this screenshot during play yesterday, as the game cleaned up between turns. The player "hopped" off the screen and didn't return until the following turn started, leaving the black circle (its shadow) behind.
chromelugins page -- "Adobe Flash Player (2 files) - Version: 11.6.602.180, Shockwave Flash 11.6 r602" Hardware acceleration was set to "default" so might've been enabled. Will set to enable manually and watch for this again.