[mod_python] meets_conditions does not seem to work

I followed the documentation of meets_conditions and wrote the following 
handler, but it doesn't work. 200 OK is always returned, never 304 Not 
Modified.

def handler(req):
    req.headers_out['ETag'] = '"12345"'
    req.headers_out['Last-Modified'] = 'Wed, 22 Nov 2006 01:00:00 GMT'
    req.headers_out['Expires'] = 'Fri, 13 Feb 2009 01:00:00 GMT'

    status = req.meets_conditions()
    if status != apache.OK:
        return status

    req.set_content_length(5)
    req.write('hello')

    return apache.OK

Versions used: Apache 2.2.2, mod_python 3.2.8

Any idea?

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