When linking in Revit files it is common to not be paying attention to what workset is current. This is not a big deal because it is easy to pick the linked file and change the workset in the properties dialog. What is less common to do is change the workset in the Type properties as well. It is a little known fact that linked Revit file have a workset in the instance based properties as well as the type properties.
This then brings up the question of why do they have both? The reason is the same as to why when you link in a Revit file and go to the visibility graphics there is a parent file and a child file (the child file usually has a number after the name).
The reason there is a parant and an instance workset property is for campus type projects. If you have one file linked in multiple times, they can be controlled individually with visibility graphics and worksets.