Originally Posted by kovidgoyal
Use the tag editor to remove them manually in that case.
but that's exactly what I did!
Following the suggestion above (since there's not a tag editor for the "remove tags") I:
1) selected all books
2) used the tag editor for "add tags"
3) selected all the tags I want removed
4) cutted that line and pasted in the "remove tags" entry
then, after database integrity check and calibre restart, the  entries are still there
I tried to remove in the "Tag View", but there doesn seem to be a way