We had this same issue with 2008 or was it 2009 RD. Deselecting "Shift plus left click" to select image in options does not work. I can't shift select anything in regular Civil3D without it forcing me to select the image underlay.
I believe you are using MAPIOPTIONS to clear the “Shift+Left Click Image Select” check mark on the General tab. If you have installed AutoCAD Raster Design the similar setting in IOPTIONS overrides it. You will therefore want to clear the “Shift+Left click image select” checkmark from the User Preferences tab in IOPTIONS.