The fix to bug 15836 introduces a functionality regression.
Limiting the acceptable response types to "application/xml" results in a 'HTTP 406: Not Acceptable' error code when the service returns XML data with another Content-Type header.
This is the case for OpenStreetMap.org, which returns its reverse lookup data as 'Content-Type: text/xml'.
The original behavior was to allow any content type, and leave it up to the server to deal with the situation.
The new behavior explicitly prevents the server from returning anything other than 'application/xml' content types.
A compromise could be to send 'Accept: */xml', or to simply revert the fix in bug 15836.