Search results issues

This is the same problem I’m having since upgrading to WordPress 3.5.2 (possibly since all the 3.5.* versions, but definitely since 3.5.2) on multiple sites hosted on different hosts/servers. The boolean search within doublequotes no longer works in either the backend or from the front page, and crucially it means that half the names and/or tell-phrases that I have in my moderation filters no longer work at all, which is a particularly retrograde step in managing various malfeasants in the commentariats.