I generally have assembly drawings with the same components on a daily basis...all use the same base component. I have to toggle 'show hidden edges' on one particular component to show detail for manufacturing purposes. Typically this is not an issue, however from time to time(more so with 2011) I run into an issue where, once I toggle 'show hidden edges' they appear momentarily for a few seconds then disappear. Is there any rhyme or reason sw does this?? Have a toggled something unknowingly? I don't know, it's very frustrating as I normally have to remodel the assembly to fix the issue!