The extra action at the end after releasing your mouse button has been around for a while, it might have been fixed in 18.4 for a bit. I think it is a timing thing, the game registers a new swing before the animation for the old one is complete. It is pretty simple to let go of your mouse button a little earlier than you think you need to and finish up the last few swings with single clicks.
As for random attacks, nope havent seen that at all and i would have to agree with eXSe, time for a new mouse.