Unpriviledged users creating ticket with custom image field broken

I have a problem where an unpriviledged user creates a ticket in a queue
that has a custom image field. Regular users can upload the image fine,
but for unpriv it just shows up as a broken image.

I have traced a possible problem to the objectcustomfieldvalues table.
For some reason it seems that two rows get added to the table for the
uploaded image. One row contains all the correct information, but the
disabled flag is set. The other row is missing the ‘largecontent’ value
and the ‘contentencoding’ value but is not disabled. If I switch the
disabled values then the image shows up ok.

So is it a bug where there are two rows being created in the
objectcustomfieldvalues table for unpriviledged users?