If we have any kind of XML-RPC error then we just close the connection. We should be responding at the very least with a HTTP error code, and likely also with a XML-RPC Fault response.
This should be done with errors with regard to the XML-RPC request itself (e.g. bug 5032), and when the handler crashes.
One problem we get by not doing this is that the default behaviour of Python's XML-RPC client is to repeat the request, so we get a double crash in our logs.