Hm, this shouldn't happen and nothing has changed regarding the mouse controls. Are you sure this happens only in 1.4.0 and not in 1.3.0? It seems unlikely that this is due to the update of the game.
Viewing post in Update 1.4.0 (new content) comments
Hmm, you're right, I restored a copy of 1.3.0 and it's broken too now. Very weird -- I assume there's no "break my mouse buttons" option I might've set by mistake? Buttons are also working fine on desktop and in other games. Oh well, no worries, it's clearly something specific to my environment -- I'll figure it out sooner or later.