I have a similar problem, I created a script to write the value of a Lookup field into a Text field
Here's the code: Project is the lookup field to the Projects list, the Project Symbols is the text field tha will contain tha value of Project
$uniqueValue = $properties.AfterProperties["Project"]
$projectlist = $web.Lists["Projects"]
$item = $projectlist.GetItemById($uniqueValue)
$properties.AfterProperties["Project Symbols"] = $item["Project"]
same code for ItemUpdating.
From web (Edit Properties) it runs perfectly,
If I modify the lookup field Project in MS Word 2007 and save the script run and the Project Symbols field is compiled, and in the document library you see the updated value.
But if I reopen the document in MS Word in the Project Symbols field I see the old value not the new one.
It seems that MS Word doesn't read the properties from the document library,
if I use the Edit Properties of the document library and than reopen MS Word the field is correctly updated.
I have missed something or is a MS Word bug?