I muttered the other day about being somewhat muppettish with the progdb. Well, it went like this. While waiting at the airport for katlinel, I started to do some work on the laptop, and discovered that the PHP scripts were coming out somewhat broken. k arrived at that point, so I put it down to there not being any network (I'd disabled Airport at the airport, being at home to Mr Irony), and decided I'd worry about it later.
When later came along, it was still broken. All appeared to be working, except that the web server wasn't interpreting the PHP scripts - they were turning up in the browser verbatim. I rebooted, restarted the webserver, checked that the scripts were okay when run directly with PHP, and spent a while looking for configurations I'd accidentally changed, and didn't find anything. In desperation, I reconfigured the webserver to report its own config (normally disabled), and it was only when I went to look at that config did I work it out.
The status didn't appear; I got "No such file", because the URL began with file: instead of http:, so /server-info didn't work. Ah, wait. I'd just modified the progdb to get the /server-info URL, so the progdb URL also began with file:.
In other words, the reason why the PHP scripts were turning up verbatim in the browser and were not being interpreted by the web server was because the browser was displaying them directly, and they weren't being processed by the webserver.
Cue a few more minutes resetting everything I'd just fiddled with, and then I actually got onto some real work...