When using the wiki Search widget, I don't think it is searching and retrieving items tagged with the search term. At least it is definitely not searching on multi-word tags. For instance, we have a wiki page tagged with the item 'biology technology'. When I search for that, nothing is returned. All of the other tag searches I have used seemed to work, however, in all those cases the tag term was also present in the body content whereas 'biology technology' is not present in the title or body content of the tagged wiki page. Do you not include tags in your search tool, or is there a conflict somewhere?