Almost all the journal titles (held in "container-title") ended up in the "Title" category of the Abbreviations List, rather than in the "Journals and Reporters" category. Is this a glitch in the MLZ abbreviation filter's field population algorithm?

This actually ties in with another problem I reported in https://forums.zotero.org/discussion/32322/mlz-how-is-the-hints-file-used. With the vast majority of the journal titles ending up in the "Title" category in the Abbreviations List, rather than the "Journals and Reporters" category, the Hints file must target the "title-phrase" rather than "container-title" to have a chance at abbreviating journal titles, at the expense of article titles also being abbreviated as a byproduct. When journal titles are properly categorized under the "Journals and Reporters" in the Abbreviations List, the "Hints" file can target the "container-title" field and leave the "title" field alone.

In any event, I think we need a quick fix for this, as you are at the mercy of how the Abbreviation Filter categorizes a publication title, and you can't manually add an item in the Abbreviations List to abbreviate a journal title that the abbreviation filter dropped.