Comment 28 for bug 1394403

In case you are still interested in this, here is a "blubb" vhost definition which contains the mod_rewrite->[P] rule (as opposed to having it in .htaccess as with the "bla" vhost).

The error log then will show termination after the first
  go-ahead with proxy request

whereas the bla host will fire some more lines with index.html initiated by mod_dir.