Riot, it has been at least three patches that the attack-move bug has been around for mac players.

For those not in the know, the bug makes the player stuck in a perma attack-move mode. Meaning, you cannot move away from a target since you're always moving for an attack, ie: you're useless in teamfights. It also makes you unable to level up skills (both with the mouse and the keyboard), buy in the shop, press Esc, space, click on the "Continue" button at the end of the game. It's like you're always pressing shift. Quite game-breaking and this really needs to be adressed.

I've also noticed, if it is any help, that the bug always occurs (at least for me) after talking in the chat (but not every time I do talk in chat). Sometimes, it also disappears, although I have no idea why.