Juvenile Fiction Not Checking the Fiction Check Box on Title-Bib

Not to continually obsess over the Fiction checkbox on the Title-Bib (see also my Fiction Checkbox query post ), BUT has anyone else noticed that Juvenile Fiction titles are sneaking in without the Fiction checkbox getting checked?  I also notice the Call Numbers infrequently - yet increasingly - read "j813.6" giving us no indication as to whether the work is JF or JN.

KLAS developers, can these books be held in check? (Pun intended.)  Picking on the book that broke the camel's back for me ( DB110247 ), I see on the MARC tab there are 650 fields that have "Juvenile fiction" as a "v" subfield...

=650  \0$aApprentices$vJuvenile fiction.
=650  \0$aDragons$vJuvenile fiction.
=650  \0$aKings and rulers$vJuvenile fiction.
=650  \0$aReasoning$vJuvenile fiction.

Would it be possible to scan incoming books for such a subfield resulting in a Fiction checkbox check?  There's probably a better way - or better field/attribute - but my knowledge on antiquated MARC is very limited.

Hi, just this morning Dina discovered ~2,200 non-fiction results for queries where "Fiction equals true" is part of Advanced Search terms. She was looking for historical fiction and found these records to correct first. I asked her if this was higher than what she normally encountered (this is a usual query to check) and she said her search method were slightly different last time, but this one "definitely more though".
I sent her queries to BCS for feedback. It seems a lot to be missing the first line of defense at their level.

Thanks!
Maureen

I should clarify this: I found about 600 Title-Bib records with FI in the CallNum field and the Fiction Check Box not checked, and about 1600 Title-Bib records with NF in the CallNum field and the Fiction Check Box checked.  Having reviewed all of the FI records and about 3/4 of the NF records, I've found that most of the NF records with the check box checked are, as Dan points out, juvenile non-fiction.  Weirdly, some adult fiction, including a small batch of Scandinavian mysteries, is marked NF.  It's an adventure.