* You did specify a mod_perl1 option

  PerlSendHeader On

on a mod_perl2 environment. The mod_perl2 equivalent would be:

  PerlOptions +ParseHeaders

which does something completely different from your intention
(it's used by cgi-like stuff).

* You probably forgot to *send* the header (not sure about that).

  $r->send_http_header;

in which case the Apache/mod_perl would send its own
(after finding out there is none).

* You probably did something else in the context or apache
config what we don't know ;-)

Regards
mwa