I know about the solution given by TMA, it works. It Half-Works.
It resolves the 3D selecting problem, but it generates a truck load of lag , or slow framerate, or low fps or whatever you want to call it. The thing is, the map begins to be unexplorable after I build just a single room( with details).
I suspect mainly the textures. I think catalyst can't handle well textures ...
I turned off texture filtering from hammer, fps increased a bit , textures looked like hell, but the lag persists. Still not solved.
I made a video on youtube so you can see the problem visually ( I'm explaining what's not working)
Youtube Link