dan1son is on the ball. I forced a status of 200 and the problem disappeared for me too!
Don't know why, but this line (from Ext.data.Connection.js) throws an exception ("Access is denied.") with a status of 400:
Ext works-around the browser bug by swallowing the exception. (Not a very good practice, but I can't think of a better alternative in this case.)Code:doc = frame.contentWindow.document || frame.contentDocument || WINDOW.frames[id].document;
I'm using IE8 at the moment.