This may sound dumb, but I got tricked by this today. I had put in some new config var key:value pairs, then went to another page, and went back later to make sure I had the key names correct, and the pairs were gone.

Later after doing one on the command-line to try that, I noticed that the pairs are sorted. Basically, my new ones were buried in the list of other key:value pairs after the page was reloaded, where I expected them to be at the bottom!