The back-end storage of the settings needs re-doing. I just used variable_set/variable_get at the moment. But an upgrade path will be made available when the storage mechanism changes.
So many changes and requests have been added to, that this module has grown from a very small one to a big one… so it has been splitted in multiple sub-modules: Custom Search, Custom Search Taxonomy, Custom Search Blocks and Custom Search Internationalization (all included in the download).
This is the dev version of Multiselect for Drupal 7. This should NOT be used on production sites and is only released in order to assist with the development of the module.