In Engraving Options>Time Signatures, suppose that the numerator is set to show beat groups and the denominator is set to show note duration. Then this is what happens when the text above each measure is entered into the meter popover:
Except for the last measure, every time the number of eighth notes in a beat group is doubled, the duration of the note in the denominator also doubles. However, the value in the numerator is not halved to compensate.
Ideally the type of double whole note which appears in the denominator of a time signature should be controlled by the same setting in Engraving Options>Notes which controls the appearance of other double whole notes in a measure.
Credit to @Janus for revealing this anomaly.