My assumption is that a 'bookmark' is assigned to a single url stream.
It used to be when I would Main Menu > Play > Bookmarks and cliked a bookmark it would appear in the playlist editor and begin to play. If the editor was populated it would automatically clear the editor and the bookmark would appear and proceed with playback.
NOW, if the editor is populated, the new bookmark is 'appended' to the list and playback of the first entry starts again from beginning. If the previous entry/entries are files, playback of the bookmark will not occur until the files have played thru. A tedious work-around is to repeatedly clik 'Next Track' until the bookmark gets selected. Another annoying work-around is to clear the playlist first with the eritor's REM button and then load the bookmark. Additionally, if the previous entry were a bookmark, the newly loaded bookmark would never play UNLESS one performed the previously mentioned work-arounds.