lucy24 - 6:15 am on Feb 2, 2013 (gmt 0)

I know this answer will drive you stark staring bonkers, but it's important. Honest.

Can you provide a little more detail about what happens between
{beginning: user clicks on link or types in address}
and
{ending: server does its thing by, ahem, serving content}

I need to be absolutely convinced that you know the difference between a redirect and a rewrite. Yes, I realize you may have made it perfectly clear in earlier threads over the years. But the WebmasterWorld forums are indexed like mad, so you need to treat each thread as an island.

Even within Apache, REQUEST_URI and REQUEST_FILENAME can mean different things-- and it's the kind of difference that can rise up and bite you.