I liked immediately the idea of having hover cards, but they are sometimes annoying. When I go hover some link, a hover card appears, but it is a little bit annoying then to make it disappear. It should be enough to go away from the hover card to make it disappear, but, for me at least, it is not like that.
Topic on Talk:Page Previews/Flow
That bug is tracked at Phab:T92932. Thanks for the feedback and bug report.