Changing search view mode loses search context

Steps:

* Start from a cold visit to the search area: /news/search
* Navigate to a saved search: /news/search?search=foo (view defaults to show summaries)
* Switch to List view; end up at: /news/search?display=views-mode-list (search param dropped)

This doesn't happen in the Feeds area, though that's probably down to differences in the URL handling, since the feed is actually a node and not just a query parameter.