Checkbox has stopped working

[StuartDH]

I've built a custom field checkbox to distinguish between identified and unidentified photographs.

All worked perfectly for the first 20 or so images that I edited, but now it seems to have stopped working. When I check the box, the information doesn't appear to be stored in the DB (I save the changes then click on edit image again and find the box unchecked).

Any ideas what may have stopped it working and how I can fix it? Doesn't appear to be anything that would solve it in the maintenance section.

I'm not entirely sure what would cause the problem off the top of my head. Would you mind submitting a support ticket so I can have a look?