Depth-only pass

I want to add a depth-only pass before my forward and deferred shading. In order to do this, I bind a nullptr as PS and a nullptr as RTV. But I get huge amounts of flickering and background leaking in a static scene? Is this z-fighting? I use D3D11_COMPARISON_LESS_EQUAL. The VSs are slightly different in the sense that the depth VS uses an object_to_projection transform whereas the other VSs use a object_to_view, view_to_projection transform chain. The object_to_projection, however, is constructed by multiplying the same matrices on the CPU.