I've encountered a strange bug where a custom field called "enclosure" added to a post (which contains an MP3 podcasting URL) is getting erased whenever the post is saved. The field seems to still be there after pressing "Save/Update" but when you return to the post after closing it, the custom field is completely gone.
My client noticed this problem recently so I'm not sure when it started, but I haven't made any changes to the site recently other than update some plug-ins, which I've ruled out as the culprit (see below for the reason.)
I found one workaround that may provide a clue: if the custom field is simply added (using the button "Add custom field") and the post is not re-saved afterwards, it does not get erased. So it seems like it's definitely the act of saving that is causing the erasure. This workaround is not practical in the long term as occasionally my client needs to go back and edit the post, and the enclosure then gets erased and does not correctly appear in the podcast feed.
I can add custom fields with any other name besides "enclosure" and they don't get erased.
I've tried turning off all plug-ins, but the problem persists.
Two additional strange things:
1) I noticed this Trac history which at first sounds related, but in my case the same MP3 URL is linked to in the post itself, so perhaps it's not the same issue.
2) I have the same site (same custom theme, plug-ins) running on my test server, and I do not have the enclosure erasing problem. I can edit posts there and the enclosure stays, as it should. Both test and live site are on the same server and running the same version of WP (3.3.1). I can't think what the difference could be that might cause this issue.
Thanks in advance for any ideas.