I’ve been wrapping my mind around this for some time now, and I#ve tried a lot…
All I want to change is the header height, so I change it in the settings an simply hit ‘save changes’ at the bottom. But all that happends is options.php file to start downloading. When you open this using the editor theres some text in it, that service is unavailable.
That behaviour is usually an indication that your WordPress is running on a weirdly configured hosting server (POST variable limits too low, issues with some characters like apostrophes, quotation marks in input fields).