TL:DR is,
The Inability to Highlight/Click on cards found in the opponents hand if it resides next to a '2Step' animated cardback.

By '2Step' I mean most cardbacks that don't animate till the mouse curser is hovered over/near them i.e the Transformers, Werewolf or Angel Sleeves.
(Doesn't work with cardbacks like the Fblthp, one tho, i.e cardbacks that don't fully change/transform the cards in some way and just move it or play particle effects)

To reproduce this effect, cast a card that lets you partially look at there hand and try and click on the left most revealed card. i.e. with Duress or Mind Spike.
(Unknow of full list of buged Sleeves, and if there hand size at the time plays a factor.)

(PC, non-steam)