--(I've hacked the system so that the content type handler returns nothing, and I receive the text/plain header, not the text/html default I would expect).
That's the track I'd try to follow - looks like a very promising way to come closer to the problem, actually already reproducing it...?
No, I haven't seen this sort of behavior yet, but I'm interested and will be happy if you would update this node with your findings if you succeed to track it down.
Did you maybe try to post the question also to the
modperl@perl.apache.org mailing list ?
Might be another good place to reach the people that might help.
TiA