So if you’ve come across the problem where users will download a document previously upload which has metadata tags against it, they will rewrite the whole document and upload but the old properties and metadata properties have been set from the last document.

Fortunately its a feature that can be disabled however not through the UI. This can be done either using SharePoint Manager or creating a feature in Visual studio which will update the property on the SPWeb.

The property is:

MSDN link:

You can also read up on Document Property Promotion and Demotion:

In a simple feature you can disabled it using the following: