global $object = undefined method warning

I've run into a slight issue with wordpress plugins, where I use the global database object ($wpdb) for queries.
it works fine, but PHPStorm highlights all methods (e.g. $wpdb->get_var() ) as undefined and also does not offer code completion for the methods or properties.
jumping to the declaration of $wpdb (cmd-b), points to the wrong location: a file (/wp-admin/includes/schema.php) where $wpdb is included as global, but not where the object is created or the class is defined (/wp-includes/wp-db.php).

is there something I can do to fix this behavior, or is this an issue for the tracker?

any help appreciated.