Calibre adding extraneous Series names

For the past few versions of Calibre (since at least 2.52), when I drag and drop new files onto my Calibre interface and it adds the books to my library, it will sometimes add an extraneous Series value to the metadata. The value is usually the last word (or the last word before a colon) from the title and is always the first in the series (although that's probably due to the lack of duplicate final words). See the attached picture for an example.

I haven't added any new import rules that I recall and I know it didn't do this when my Calibre version was in the 40s (my last version prior to 52). Thoughts? Suggestions?

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