nah, just do
sc_screen_default->settings.forward.enabled = 1; //enable if you need particles or custom materials which can't be rendered in the deferred pipeline
sc_screen_default->settings.refract.enabled = 0; //enable for refractive effects such as heat haze and glass
and you are good to go.
Maybe its a bug, I don't know.. this will happen if you don't use some of shaders from 'common' folder. F.e. try to place a volga car with it's material (look up 02.wmb from shade-c folder).
Edit: did you assign any shade-c material to level geometry? Maybe that's causing it too..