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I won't post a complete test here, but I would mention that I'm using the Ext.ux.UploaderDialog and it uses this component. I've met a problem on uploading an image bigger than the allowed size for upload, so I got a regular 413 Status message and still got an "ajaxsuccess" message. I think this should be an "ajaxfailure" rather than a success message. The case is that I got a regular HTML message as well with the 413 status code (ngix) so maybe that can be a problem as well.
Does anybody encountered a similar problem or point me to a direction where I get a better solution?