"Ask - Recent only" means just that, they are only written to the recent bookmark list. If you choose "Ask" it will also create a "local" bookmark file (which is located in the parent folder of the audio files; the same folder for playlists). I can understand if the manual is a bit unclear about this...
And the code could be improved too, it seems. If I read it right, if you set bookmarking to "Ask - Recent only" (or "Yes - Recent only") and then disable "Maintain a list of Recently Used Bookmarks", Rockbox will happily say "Bookmark Created" even though no bookmark was written.
To get more than 10 recent bookmarks, you need to change the code. An easy change though.