MSW: when I load the level it looks as expected, when I apply the lightmap for that level (that it was loaded with, I reload it as a texture) and apply that to the same level it gets screwed up.
Yes I fully realise that...what I have been asking is once it gets screwed up, can you at that point apply the original lightmap that was loaded in and have it return to the way it was?
Make a copy of your complex level .B3D file...in this copy strip out the refrence to the lightmap so that it doesn't load it with the level...if you can't do that then make a copy of the level textures, open them in some image editor and reduce all of them (except the lightmap) to half or quarter thier size (if they are 512 X 512, reduce them to 128 X 128 or even 64 X 64) set it up so the level will use these smaller test textures...or set up the graphics to run in 320 X 240 X 16 or 32-bit mode...
then use your example demo to load the level and two copies of the lightmap...then run that.