The calendar widget can be scaled down too far. It has a defined minimum size and therefore doesn't break when being scaled down, but the month table isn't readable at all anymore. The numbers just disappear. Reproducible: Always Expected Results: The widget's minimum size should be a little bigger so that the month table can at least be read with a magnifying glass.
Seems to be fixed in 4.8.97. The defined minimum size is not too pretty, but the calendar is still usable (although the weekday names are very small).