Changes to JSONP callbacks

Hello!
Why the callback param doesn’t work for access_token method anymore?

For example, the command
http://api.twitch.tv/api/channels/channel/access_token
returnes the valid response for stream called channel, but the commend
http://api.twitch.tv/api/channels/channel/access_token?callback=foo
returns foo({“error”:“Bad Request”,“status”:400,“message”:“Bad Request”}), although it worked earlier