The portlet "Wiki Display" (not Wiki) has, by default, a search tool rendered at the top of the content area.
When you use this tool and press "Search", the portlet is no longer rendered on the page – it just goes blank. I believe this has to do with the purpose of "Wiki Display" as a portlet to simply publish a single wiki page as content, not a portlet to give general or searchable access to the wiki.
The improvement I'm suggesting is one of the following:
1. Don't display the search tool in this portlet.
2. Have the tool present some kind of result when the search button is pressed.