The XSD file for the partial-response element states that a <partial-response> may have exactly one of <changes>, <redirect>, or <error> as a child element. This is incorrect. We should allow any number and combination of those child elements for maximum flexibility.
This problem manifests itself when the server needs to send an <error> response when some <changes> response data has already been written to the response. This can happen if there is an error during rendering.