Thread:Project:Support desk/LocalSettings.php being ignored

I've been using MediaWiki 1.23.6 for the last few days. I tried to change the logo without success and assumed that I had the image path wrong. I now realise that ANY changes I make to LocalSettings.php have absolutely no effect at all - in fact, I can delete the file and my wiki runs just fine without it.

What's causing this and how do I fix it?

I'm running on localhost with XAMPP, PHP Version 5.5.15 and MySQL 5.6.20