Can't delete "New symbol" from "Edit Music Symbol List" dialog

I don’t know how, I have a lot of “New symbols” in the “Edit Music Symbol List” dialog that I can’t delete…

I have also opened the userlibrary.xml file trying to delete them from there with no success. By the way, I have found a lot of composite definitions in this file that are not longer used in Dorico… Is that normal?
Thanks in advanced!

I guess those “New Music Symbol” entries will be related to playing techniques and/or accidentals that you’ve created in other editors within Dorico. They’re harmless, though of course I can imagine they’re a bit annoying!

Thank you Daniel. It is probably so, but currently they are not used in my score… it seems that they are a kind of “ghost” symbols that remain undeleted when the technique that origitated them is already deleted… I am worried because now they are only a few, but if I keep editing, they may become a lot…