I found a neat turtle dragon bug. If you get your TD submerged, then your opponent has his Dust Devil do the Dervish thing, the TD ducks (adorable, btw), but the card below comes up. Both cards (TD and the one below) occupy the space. You may have to click a couple of times to select either one.
That sounds like a coding nightmare, but does seem like it shouldn’t be hard to nail down where the issue is!