I'm having this issue on several server environments.
We have a list at the site collection root. There is a site column created as a multi-value lookup on that list's Title field. This site column is used in document libraries in subsites as a required field. When we upload anything but an Office 2007 document, the user is presented with the document metadata fill-in screen (EditForm.aspx?Mode=Upload), the user fills in the appropriate data (including picking a value(s) for this lookup), and clicks "check in" - the document is checked in as expected, with the lookup field's value filled in.
With an Office 2007 document, this fails. The user selected values for the lookup field do not ever make it to the server - no errors are thrown, but the field is not saved with the document. We have an event listener on these document libraries, and if we inspect the incoming SPListItem on the event listener method before a single line of our code has run, we see that the value for the lookup field is null.
It smells like a SharePoint bug to me - but before I go calling Microsoft, has anyone seen this & worked around it?
Edit: the only entry I see in the SP trace logs relating to the problem:
CMS/Publishing/8ztg/Medium/Got List Item Version, but item was null