Document library forces check-in upon adding custom lookup column

Question

1. SharePoint 2007 Team Site
2. Add a Document Library with the Word 2003 template
3. Add a new item, save, close document, no problems
4. Add a (required) custom lookup field to the document library
5. Add a new item, select lookup value, save, close document, problems

After step 5, when I return to the doc lib, the item appears to be checked out and the lookup field value has not saved. I then have to edit properties and set the lookup value before it will let me check it in.

By default, the option in Document Library Settings -> Versioning is set to "No" for requiring items to be checked in and out. Toggling this option has no effect on the above behaviour. I've also confirmed that a regular Choice field, even if required, doesn't cause this behaviour. As far as I can tell so far, it's only the Lookup field that does it. Also, this behaviour occurs at every site level.

I've search online a little bit and didn't find anybody else with this issue, so I suspect it's a conflict with our Office integration, but I thought somebody on here might have a more specific idea.

Thanks!

Answer 1

Resolved the issue.

I was using the field name "Category", which I guess might have obscured a site column with the same name. SharePoint must have been looking for the site column and finding the custom lookup field, or vice versa.

TL;DR: Don't name your custom lookup column "Category".