To reproduce:

1. Embed a calendar in a wiki page using "week view."
2. Create a 1 hour (or longer) event that is not an all day event.
3. Hover your mouse over the lower middle of the event (your cursor will turn into a small down arrow).
4. Click and drag downward, as if to lengthen (add time) to the meeting.
5. You will notice:
   • your meeting has not been extended.
   • your meeting has actually been reduced to a half hour.

I'll try to attach a screen video soon.