I have noted that similar things are mentioned in other posts, but could not see it here.
When rendering a scene for the second (or more) time, the radiosity is way off - everything appears to be over saturated. By pausing the rediosity process then restarting, you notice a considerable change to the rediosity image and this has the same effect with to the final render. Why should this be the case??
The pause/unpause trick does not always work however, and eventually you have to shut the program down and restart to get the scene to render correctly.
In addition, ceilings render black if recessed down lighters are used and radiosity quality is not over 3