Office Issue: Document Information Panel


I'm using Version 1.0 and got the following issue:
Mainpage with List "Demo_List"
Subpage with Documentlibrary and Custom Field "Demo_List_Column" of type "Extended Lookup" with Items of "Demo_List" on the Mainpage.
In the DocumentLibrary I can edit and change all Documentpropertys and the extended Lookup works great. But in the Office Document Information Panel I see a String-Field "Demo_List_Column".
I can't change anything there, and the Field is filled with the following text: "Edit property on server".
So I can't use the Lookup in Office Documents and must change or set the Propertys of fields with type "Extended Lookup" only in SharePoint.
I tried to edit the fldtypes_*xml like the following blogentry told me: "http://nickgrattan.wordpress.com/2008/01/06/sharepoint-2007-custom-fields-and-edit-property-on-server/" but this doesn't solved the problem.
Could you have a look? If you can get this to work, your Lookup would be perfect!