We needed to disable a Rails site for a little bit and figured
PassengerEnabled off and a little bit of apache mod_rewrite would do the trick in the least painful way ... but Passenger refused to turn itself off and kept serving our (slightly broken) rails app!
After some hours of bewildered searching and starting to doubt our sanity, we found the culprit:
PassengerHighPerformance on - cut that line and
PassengerEnabled off works as advertised.
This is not even slightly Phusion's fault, btw -
PassengerHighPerformance is clearly marked as experimental and flaky in their excellent docs. What we need to do, in the general case, is figure out a foolproof way of advertising the presence of a potentially buggy option in our config files (whatever the software product is) so it's easy for any team member to eliminate likely causes of incorrect behaviour when the bug-hunt is on.
This article is a start, I guess :)