I have several pieces of custom meta-data. I had included a "synopsis" item so I could look at the synopsis while I was entering other meta-data, but that really didn't work out; it was easier to include the synopsis in the outliner view I almost always have open.
So I deleted it.
The outline had shown Title & synopsis, month, day, year [custom calendar that does not fit Gregorian], keywords.
After I deleted that custom meta-data field, the outline suddenly showed Title, word count, label.
That was unexpected.
Worse: the field selector dropdown still shows all the fields previously shown as still selected.