the Services module's node.save service does a drupal_execute() call on the node form. when the content type is set up to use Mnb buttons, it ends up doing a redirect - the same one it would normally do if you click on "Save". this makes the xmlrpc POST to the server return a 302, so that it tries to redo the xmlrpc call to the node's URL, which does not work so well.

i don't know what the best way to deal with this would be. i added a line that tests to see if $_GET['q'] contains 'xmlrpc' and skips the redirect if it does. that got me past the problem i was having, but isn't exactly what i would call a robust solution...