Here’s what I did: I created a standard cube, put SubSurf on with Subdiv 2. Than I rotated the view like in this Image.
In z-buffer mode with Limit Selection to Visible on I tried to select the left face of the cube. Trying to select the face directly didn’t work, I had to select right from it. It looks like selection takes place using the Optimal setting for SubSurfs. Also When switching to edge selection the back-edges on the cube can still be selected.
Is it a Bug or a Feature? Let me know