When rapidly left and right clicking in tandem (to replace one type of block with another) if the clicks are too close together, the second is ignored and the first is "sticky", performing that action (e.g. breaking blocks) without any input from the player.

You have to press the afflicted button again to get the game to recognize that the button was, in fact, released.

https://youtu.be/nCEPwgO-GGc