The custom renderer (implementing ISimpleBlockRenderingHandler) has in its renderWorldBlock function the same code as the RenderBlocks (the vanilla renderer) renderBlockLadder function, only with a second face for each metadata (to render the back face).
The other functions are basically empty (renderInventoryBlock is blank, shouldRender3DInInventory returns false, getRenderId returns the render ID assigned to it, via the base mod file).
So I don't know what you're referring to.
Full render class.