I noticed today that your caldav Python bindings can no longer load events using event.load from davical v1.0.1. Further investiations revealed that it is because davical now checks that there is XML content if the Content-Type is set to (application|text)/xml This extra checking was added in December of 2011..
For most queries from caldav the Content-Type is set to text/xml, regardless of there being any content in the body.
The attached patch removes the Content-Type if there is no body. This gets things working against davical again.