I was trying to organize the favorite queries by their url (newer queries have bigger numbers in the url). I noticed that when I unstar and then star several queries, they do not effectively get unstarred; multiple copies start to exist. Please check https://quarry.wmflabs.org/query/11613 and https://quarry.wmflabs.org/query/11685 .
Topic on Talk:Quarry
It's recommended to report this bug in http://phabricator.wikimedia.org