I think what he means is that opening something view only actually sets your system options so that the next time you open something it's lightweight. That shouldn't happen.
I'm on 2008sp3.1, and I see this behavior as well. It is pretty annoying, because there seems to be some bug such that no matter what my performance/large assembly mode settings are the "lightweight" box is grayed out in the Open dialog whenever I select an assembly file or a drawing of an assembly. Sometimes it's checked and grayed out, sometimes unchecked and grayed out.
-handleman, CSWP (The new, easy test)