if you have a cbz/r file that is not working, open a ticket and attach the file. Cover browser is really just a "cosmetic" feature, eventually I will implement a cover based table view for browsing your collection by covers. But yes, if you type a search query first, the cover browser will only show the covers of books matching your query.
As for a roadmap, calibre is developed so quickly that maintaing a roadmap is pretty pointless
