Like i said in my initial replay, the code change is only a part of it. in the Data Assist Search behavior, you need to make sure that the criteria use the Keyword type, and set the Or seperator to use a comma and a space:
", "
", "
open the results page. go to the server behaviors panel and Doable Click the Data Assist search server behavior. Edit each criteria that uses a multi select list, set the Criteria type to Keyword and the set the OR separator to:
", " (without the quotes)