We have an ASP.NET web application which is mapped to a folder on an apache hosted php site using ProxyPass.ProxyPassReverse.
A couple of problems being encountered.
cookies are being lost which breaks the site navigation, this can be overcome by setting the asp app as cookieless.
Forms authentication is used on the ASP site, this is also broken withe the proxypass in place, suspect this is cookie related also.
ASP site works ok when run from a domain/ip address.
Use of a separate domain / sub-domain is not an option duew to client requirements.