Couple of threads on http://wordpress.org/support with people commenting that they don't seem to be able to display tweets from lists - eg http://wordpress.org/support/topic/how-does-one-show-other-people-tweets-list-or-other-account?replies=5
Looking through the code the cause appears to be here - if there's no screen_name specified but there is a list_id then it gets the user, sets the appropriate oauth token but then requests the user's timeline instead of the list data.
Fixes bug where it's not possible to fetch statuses from a list
Nice catch. Thanks for that.