Worth reading this http://msdn.microsoft.com/en-us/data/jj573936,
"When results are returned from the database, objects that do not exist in the context are attached to the context. If an object is already in the context, the existing object is returned (the current and original values of the object's properties in the entry are not overwritten with database values)."
the load and reload methods are worth a read too. Sounds like you want that behaviour.
http://msdn.microsoft.com/en-us/data/jj592911.aspx
http://msdn.microsoft.com/en-us/library/system.data.entity.infrastructure.dbentityentry.reload(v=vs.113).aspx