I have developed an add-in for Word 2007 which prompts the user for, and then sets, some Custom Document Properties, and then saves to a selected document library in Sharepoint.

When the destination site is NOT in my list of trusted sites in IE, I am prompted for user credentials, as expected, and the document is saved correctly with all custom document properties being transferred to the server properties in the doclib (which is what I want).

When I add the site to my trusted list, I am not prompted for credentials, but none of the custom properties are transferred even though the document is saved.

My assembly is in a trusted location. The created document is in a trusted location before it is saved to Sharepoint. Am I missing something?