The script never sets a status to that manually, so it must be coming from twitter itself. Though the script is pretty buggy at this state, since Adium decided to change the model on how statuses work :(

Does it happen all the time or just occasionally?

You could try now with the new version 1.3. Hope this helps!

Try now with version 1.3, if you still have issues, reply here. I always read comments and aware that it might not be working.