When you have silhouette edges turned on (under Graphic Display options) in a view in Revit 2010, you cannot “Override Graphics in View” by Element or by Filter as you did in Revit 2009. The override ends up being behind the Silhouette rather than overriding it.
What really annoys me about this bug is I have been trying to spend a lot of time ensuring users are producing good looking drawings with appropriate line weights. When using Silhouette you can still individually line work each line, but having the option of using filters or overriding items by element to change line work is very powerful a large repetitive elevations.
Autodesk have been made aware of the problem and have passed it onto their development team.
The best work around is to use the line work tool and specify the desired line style.
Problem exists on Revit 2010, including SP1 and SP2