There are a number of known issues with the Multilist With Search field type, such as showing separate records for the numbered and language versions of the same item, freezing on the first load, and failing to parse some kinds of field sources.
While many improvements have been made to the Multilist With Search functionality in Sitecore CMS 7.2 Update-6 (rev. 160123), it might still not provide enough means for searching and filtering.
When facing any issues related to the Multilist With Search field type or requiring additional filtering and sorting functionality, you can use the Advanced Search List field type as an alternative.
For more details and instructions on how to enable it, refer to the release that is compatible with your product version and can be found on this page: https://github.com/sitecoresupport/Sitecore.Support.AdvancedSearchList/releases.