When viewing documents from SharePoint in Microsoft Office, you have the ability to change the metadata for a document using the Document Information Panel. Lookup columns to a SharePoint List are represented in the Document Information Panel by a dropdown control, with the text of the selected value displayed.
You may notice sometimes that the text of the selected value does not display, and instead a numeric value is shown:
This is due to the configuration of the default view of the referenced SharePoint List. The selected value for that field on the document extends beyond what is configured for the Item Limit for that List. Raising the Item Limit to include the selected value will cause the text of the selected value to display as expected.