Hi Svilen,
FYI:
https://rails.lighthouseapp.com/projects/8994/tickets/5277-rails-300rc-responds-strangely-to-empty-accept-header https://rails.lighthouseapp.com/projects/8994/tickets/5278-order-of-an-accept-header-should-not-matter-to-respond_to-rails-300rc
I believe that rails is doing the wrong thing here, but I do not have time to supply a patch.
best, Erik Hetzner