Does someone have a solution to this now....
I have been looking for a answer to this problem also, the thing is I know my faces are co-planar because after it happens i can turn on hidden lines and delete the triangulations without losing my surface.
Triangulation does occur from the intersect faces command as mentioned above however in some situations if I try to create an opening in a surface by drawing on the face with a rectangle or lines (my usual preferred method) then it does not cut any hole and also creates more faces across the entire surface (usually 2 extra surfaces on top of the original) in the same plane.
My firm recently moved to 2013 from SU7 and it is definitely has more bugs and issues while being slower to run in general.