It looks like (to me as someone who has no clue about coding) there was a new bug introduced with Super Cache 0.9.3 related to Windows Live Writer (WLW).
If I try to edit an existing post with WLW I get the following error message:
The response to the metaWeblog.editPost method
received from the blog server was invalid:
Invalid response document returned from XmlRpc server
I've uploaded the detailed error log from WLW here:
http://tinypaste.com/8f945
This happens only when Super Cache is active and didn't happen before Super Cache was updated to version 0.9.3.