Radiosity: deleting the light dome makes model white

I am doing a radiosity render, based mostly on the tutorial in the manual. The manual says once the radiosity calculations are done, you can delete the vertices in the new mesh that used to be the dome object.

But when I delete these dome faces, the model loses all of it’s shading and is pure white.

What am I doing wrong?

I can get good radiosity renders… if the dome is still en-tact.

Ok, so I tried deleting the dome pieces again, this time by paint brush mode selecting the faces, and chosing delete faces… and this time it worked!

So I am not sure, maybe you cannot select the faces, and then choose delete vertices?