When searching for a page title with a colon in it, it is a very common to typo a semicolon instead.
When the target is a page in the main namespace, the search engine usually finds the intended page (e.g. searching for "Star Trek; Voyager" (with or without quotes) the search engine finds Star Trek: Voyager as the first result).
However when the intended page is a shortcut (e.g. MOS:HYPHEN) or page in another namespace (e.g Template:Unreferenced) and you use a semicolon instead of a colon then the search results don't feature this.
In all cases, the drop-down search suggestions do include the non-main namespace pages, but these are not available in all environments and not used in every place they are available.
The ideal solution I think would be to place a link as a "Did you mean" entry. For example if you search for Template;Unreferenced the search engine results would be prefaced by: Did you mean: Template:Unreferenced
I'm undecided whether this should apply only to exact matches - should searching for Template;Unreference (which doesn't exist) do as it currently does, or ask "Did you mean: Tempalte:Unreferenced" as is currently the case if you search for Template:Unreferece
In all cases if a page name exists with the semi-colon this logic should not interfere with taking you to that page (e.g searching for Help; a Day in the Life should take you to that redirect, not search for a page in the help namespace)