Calendar blocks can end before they begin
Create a new block on the calendar. Make your start time later than your end time. Save the block.
The software happily accepts what is clearly an erroneous entry.
Worse ... blocks with the same start and end time or with and end time before the start time ... create an unstable calendar.
With such blocks created users experience erratic behavior of the calendar:
* software locks up when displaying a week
* appointments don’t appear
* blocks don’t appear