Issue #12133 introduced a patch which seems to cause problems.
I'm using Python 3.2.1 on 64-bit Arch Linux (this version already incorporates the changes from #12133).

The following code:

with urllib.request.urlopen(url) as page:
    pass

raises "ValueError: I/O operation on closed file." exception when url is "http://www.imdb.com/".
When I removed "h.close()" (added by the patch) from request.py everything worked as expected.
Other URLs work flawlessly with patched code ("http://www.google.com/" for example).

Maybe it is something to do with differences in HTTP responses or in server-side behavior.
For example IMDb's "Cneonction: close" (not a typo) feature.
But this could be totally unrelated, I am by no means an HTTP expert.