Culling masks in deffered lighting

Hi,

According to unity's page about deferred rendering :

http://unity3d.com/support/documentation/Components/RenderTech-DeferredLighting.html

It says : "Disadvantages : ..... limited support light Culling Masks".

I would like to know more about this limitation. I'm guessing that culling mask doesn't get stored in the G-buffer, so dynamic lights can't know if a pixel is supposed to be lit by them or not. Is this the case? If so, does the "limited support" mean that baked lightmaps are still able to mask-out objects using culling masks?

Thanks!