Tried your plugin and many other Post-to-Twitter plugins. And i've noticed a common issue: They all end up firing a twitter post that says "Auto-Draft" when posting via XMLRPC clients (WP Mobile apps, Live Writer, and such).
It's worth noting that in WP-to-twitter's case, this behavior also occurs even if I uncheck the option to tweet when publishing via XMLRPC.
Reading further in many threads, there seems to be some sort of 'auto-draft-to-publish' post transition state in posts created by XMLRPC clients.
Maybe you can take a look?
Thanks in advance.