It doesn't have anything to do with the mod. To the left planet/unit interface (where you build structures), their is a big (I think it's yellow but I can't remember right now) button that turns on and off automatic structure placement. You must have accidently push it sometime, and pressing it again will allow manual placement.

Aye it is yellow, just above the ping button. It has the shape of an infinite sign with a little polygon ontop of it. I belive there is also a hotkey that turns it on and off, but I cant remember what it is.