Just updated rails to 4.0.1 and it seems to no longer respect the Accept header. All pages render in html by default and my json resources trigger an UnknownFormat exception. I've had to resort to manually parsing env['HTTP_ACCEPT'] and setting request.format myself.
Could you create an example application to reproduce this bug?
hm.. doesn't seem to happen on a new rails app. I don't understand why it would suddenly not accept json on my app though. I guess I'll do more digging.