When viewing a calendar that has a lot of events, it sometimes displays the start date incorrectly.
For instance, Gina and Tina Rae's vacations both start on July 14th, but the calendar is showing them as starting on July 15th. If you hover over their events, it says their vacation starts on July 14th, so I'm confident the data is correct.
If I change the filter to only show Gina's (or Tina Rae's) department, the event displays properly:
Stephen and Natalie's vacations correctly show as starting on July 14th.
I suspect the issue has to do with Allyson and Evan's vacations ending on July 14th, which is triggering the programming logic to fill the gaps incorrectly.