If SSL is enabled but non-ssl to ssl redirects are disabled, the server answers with status "200 Bad Request" (and an error message suggesting to use https), which triggers certain proxy scanners (and banned my bot from euIRC). It should be "400 Bad Request" or "200 OK" as defined in the HTTP standard.
That proxy scanner seems rather overzealous if it is rejecting HTTP responses just based on the message. However, I will change this to "200 Document follows" which is what Webmin uses for regular pages, in the next release.