I recently experienced some very strange behavior on a client model. Three "categories" for one element. You might be thinking: Impossible!
One does however stumble across some strange things in Revit, with some of my favorites highlighted in Luke Johnson's blog: What Revit Wants.
Getting back to the "three category element" though - While doing a bit of family maintenance on a project, I came across these diagonal lines: Looks like Reference Planes, right?
Not really.... Revit sees it as Linear Dimensions....
When navigating to a referring view, however, they are seen as camera views... Has any reader experienced this yet, and even better: Found the reason?