MARC batch edit appends instead of adds new tag if other iterations of the tag are in the bib record

Discovered in 2.2 (master)

We attempted to add tag 856 with a particular $u and $y URL and public message to a group of bib records. It was fine if the records being edited did not have any pre-existing 856 tags, but if 856 was present, instead of adding our new tag separately, the $u and $y and their values were appended to all the existing 856 tags.

What we wanted:

=856 41$uhttps://acorn.biblio.org/eg/opac/results?locg=1&bookbag=60328&sort=pubdate.descending$yTo see other titles in our catalog that have won the Nutmeg Award, click here.
=856 41$3Publisher description$uhttp://www.loc.gov/catdir/enhancements/fy0742/2006032689-d.html
=856 41$3Sample text$uhttp://www.loc.gov/catdir/enhancements/fy0745/2006032689-s.html

What we got:

=856 41$3Publisher description$uhttp://www.loc.gov/catdir/enhancements/fy0742/2006032689-d.html$uhttps://acorn.biblio.org/eg/opac/results?locg=1&bookbag=60328&sort=pubdate.descending$yTo see other titles in our catalog that have won the Nutmeg Award, click here.
=856 41$3Sample text$uhttp://www.loc.gov/catdir/enhancements/fy0745/2006032689-s.html$uhttps://acorn.biblio.org/eg/opac/results?locg=1&bookbag=60328&sort=pubdate.descending$yTo see other titles in our catalog that have won the Nutmeg Award, click here.