Can't remove Prefix markup

It’s possible that I’m losing my mind, but I can’t remove the Share Prefix Markup. I entered the word Share in the Share Prefix Markup box and it showed up as expected. But then I changed my mind and I want to remove it, so when I remove it and save it does not go away when I reload the page. Is this a bug or am I just tired?

https://ww.wp.xz.cn/plugins/social-media-feather/