This is really annoying, hoping there’s a work-around: hit the command-H, what you’d expect is the search/replace dialog, what you get is a hidden MonoDev window! It’s an accelerator on both the MonoDevelop ‘program’ menu, and the Search menu. New in 3.4?
Found work-around: MonoDevelop menu, preferences, key bindings, look for Search options then reset Find to (say) control-F and Replace to (say) control-H, more consistent with other os’s anyway