With the latest release (13.23) the image before and after the marked picture are still getting marked as favorite while not actually marked.
Screenshot of the next picture being marked as favorite with the star while not actually being marked as favorite.
Contrary on re-opening the viewer the actually marked picture doesn't get marked as favorite (but going one picture either forward or backward will show the favorited icon):
Re-opening the next/previous picture directly will not mark them wrongly as favorite (but marking a new picture as favorite or navigating over a favorited picture will consistently reproduce the bug for me).