By enabling WP_DEBUG inside your wp-config.php you’ll notice several errors within your plugin code:
Function form inside the MinitwitterWidget class doesn’t initialise the variables of the $instance:
function form($instance) {
$instance = array_merge( array(
'username' => ''
,'limit' => ''
,'list' => ''
,'query' => ''
), (array)$instance );
?>
Same thing with the widget function within the same class. This won’t even show as an error, since as soon as you instantiate the widget into a sidebar it’s default values are saved. At least check for empty(). BTW if you have WP_DEBUG turned on the default values are the error notices!
Thank god that shortcode_atts() deals with this on its own.
And the last one – this line: add_shortcode('minitwitter', mtf_create_shortcode); should have quotes:add_shortcode('minitwitter', 'mtf_create_shortcode');, otherwise the second argument is considered an undefined constant, and yields an error notice. It’s a notice, since undefined constants default to their names as strings.
Cheers.
