The first portion of a search results page --Matching pagenames-- is ignoring the restriction of a search to a namespace.
For example, this search of the term "css" restricted to the namespace "devel" at www.dokuwiki.org:
returns this list of "Matching pagenames":
* css (devel)
* css (faq)
* progrecss (plugin)
* code_css (tips)
* css (de)
* css (fr)
* css (ja:devel)
* css (ko)
of which only the second one satisfies the search restriction; the others should not be present.
(As a related request, the message "You can find the results of your search below." could be improved by adding some mention of the fact that these results have been restricted to namespaces such and such.)