I have noticed that Shortcodes UI button sometimes vanish in Visual Editor but thought it was a conflict or something. Seems to happen when I add or remove own code via functions.php.
Now it did it again and I searched for "reset TinyMCE", going back like removing code does not help - ended up here http://wordpress.stackexchange.com/questions/36583/tinymce-is-broken and voila.
define( 'CONCATENATE_SCRIPTS', false );
made it come back instantly. I dont know if this is a cache issue or real conflict with how WP bundles backend stuff. I will let it stay this way. Probably a local problem but who knows.