It's actually even simpler than that - we can just go back to ignoring the __loader__ attribute entirely and always searching for a new one, since we want to pick up changes to the import hooks, even for modules with a __loader__ already set (which is almost all of them in 3.3+)

I'm not sure it's worth fixing in 3.3 though, as opposed to just formally specifying the semantics in PEP 451 (as noted on python-dev).