the rewrite/proxy has been working for long, and I've done many tests on this function in the past. I'd share more experience after you've got it working, for example, how to get it working with cache in rewriterule.
please check if you've defined proxy context at the same time.
if so, best to delete them to reduce conflict. forgot to ask, if the virtual host defined in lsws admin console(i.e., native vhost) or come from apache's httpd.conf ?