To get around it...
Click <ctrl-shift-B> to open the bookmarks list.
Right-click each bookmark and RENAME...
Note the boxes next to bookmarks 1 and 3.
When they are renamed those boxes will vanish and Split at Bookmarks will work correctly... 
Bookmark tests here did not cause the issue. Perhaps when created there name labels were somehow corrupted.
For each bookmark added, the clip name and unique time were automatically written - like this... 