Application errors give 200 response in production

I've noticed a problem with all my sites recently that an application
error gives a 200 response and the "Application error (Rails)" message
rather than the contents of 500.html. This can be any kind of error
such as NoMethod, Syntax error, RecordNotFound etc.all of which you'd
expect to result in the 500.html page and a 500 response.

I was able to confirm that this happens both on my production server
(lighttpd+fastcgi) and on my development machine with either mongrel or
webrick. It also happens with any browser/operating system combination.

I set up a brand new rails site with nothing but a controller with one
action. I put a deliberate error in that action and was able to confirm
that the problem still existed, ruling out any problem with my
aplication code or plugins.

My Rails version is 1.1.6

Many thanks

Just tried Rails 1.2RC1 and this has fixed the problem.