Lighttpd

Ruby on Rails uses 422 to denote (validation-)errors when saving a model and the documention suggests to send an XML document (if an XML document was requested) containing the errors.

<errors>
  <error>I got error'd!</error>
</errors>

The ruby gem ActiveResource relies on this behaviour. This body is removed by LightTPD as it is flagged with 422 and connections.c does not contain a case for 422.