Minimap camera & culling Mask

I have put all of my scene lights into layer 8 which I've called 'All Lighting'. Now I'm trying to hide layer 8 from my Minimap camera. In the camera's Culling Mask, I've selected 'Default' only, and not 'All lighting' (layer 8). My problem is that the minimap camera is still showing all the lights. How do I resolve this? I'm obviously not understanding something basic here :)

Many thanks