Ghosts or Shadows on your barrel ceiling?

Residents have seen ghosting or shadow marks appear on the ceilings of rooms with barrel vaulted roofs.  I have been sent photos (below) of one example.  I understand this is not an isolated case, and that others have reported seeing this too.

There are a number of theories about the cause and what to do about it, but if you see this in your flat contact the BEO for advice.

If you have had this problem in your flat and have fixed it, please let me know how you did it so I can put the information here on the blog for others.

Click the image for a larger view