The blank background field appears to be browser-dependent. Everything
I've described in previous comments was done with Opera. The background
field is not blank when I use Firefox. I've now used Firefox to make a
move and change the background image in one of my games, and it looks like
the setting was saved.
I had a look at the source for the verification page in question, and I
think the problem is due to a missing angle bracket in the < SELECT > tag
corresponding to the background field. Also the < /SELECT > tag appears to
be missing altogether, but this doesn't seem to cause problems for either
of the browsers I've tried. When I edited a local copy of the source,
inserting the missing angle bracket was enough to make Opera place the
appropriate value in the background field.
I had a look at the source for the verification page in question, and I think the problem is due to a missing angle bracket in the < SELECT > tag corresponding to the background field. Also the < /SELECT > tag appears to be missing altogether, but this doesn't seem to cause problems for either of the browsers I've tried. When I edited a local copy of the source, inserting the missing angle bracket was enough to make Opera place the appropriate value in the background field.