At least a year ago, I ran into this guy’s problem. Today, I just ran into a similar situation with Rails 3’s class-level respond_to / instance-level respond_with pattern.
I had the following declarations at the controller’s class level:
I only wanted the JSON format for the create action, so I thought this would be pretty harmless. It isn’t. In Internet Explorer 7, the first declaration causes refreshes of the DesignsController#index action to return the JSON representation, whereas initial page loads show the HTML version. Swapping the first and second declarations fixed this issue.
I presume that the cause is the same as the linked article?