I’ve noticed that in some search results on mediawiki.org, the link to the section containing the result is a redlink.
(Note that the first result has a blue section link.)
The links point to the target page without the section, e.g. https://www.mediawiki.org/w/index.php?title=Manual:PHP_unit_testing/Writing_unit_tests_for_extensions&action=edit&redlink=1 for the first example.
So far, I haven’t been able to reproduce this on another wiki.