When you have a document library with metadata, and one of the metadata colums is a lookup to a list not all the list items are displayed in the DIP (Document Information Panel) of an Office 2007 application.

This did not happen with Office 2003 applications or when you use this is in the SharePoint interface. So I started looking around and this occurs whe you have a list item limit on that list. This is what was configured in the settings of that list (Settings / List Setting / Views / All items)

When I changed the Number of items to display to 100 this problem was solved.