searching for a way to get rid of these (i just activated an 'auto-add' folder and checked the box to mark the new additions) i came across this thread. i tried everything in here and finally gave up and decided to go back to the preference to remove the mark when a helpful tooltip informed me these are temporary and disappear when calibre is restarted.
seems a kludge, but hey! i sure don't want to look at them once i've cleaned them up.
/guy