Mongrel returns Not Modified response status if there was some changes in the headers of the page.

For instance:
I 've changed the Content-Type in order to fix a bug on browser side. But browser didn't manage to resolve that change.
It is strange that firefox doesn't have any problems and detects the header change.
But webkit inspector shows old headers values in inspector.
Maybe it is the WebKit bug or Rails bug.

But anyway I think that server should set response status to 200 in case when headers were changed.

Please, check if that could be a Mongrel related issue.