The problem with the render windows not closing has been tracked down and
is not a bug (as such) in either POVWIN or Moray, but a 'feature' of Microsoft
Windows related to the use of threads.
The easiest solution is just to instruct POV-Ray for Windows to close the
window automatically. To do this, from the POVWIN menu bar, find the item
Appearance|Render Window|Auto Close
and turn it on.
