The most important thing when it comes to web server configuration is to have a testing setup you understand and that is fully under you're control. That goes twice for working with mod_rewrite.
My recommendation: use only curl -I so caching is ruled out as a problem source. Use a virtual machine that you can reprovision quickly and reliably. Crank up the log level to debug in you apache config. And don't give up!
My recommendation: use only curl -I so caching is ruled out as a problem source. Use a virtual machine that you can reprovision quickly and reliably. Crank up the log level to debug in you apache config. And don't give up!