Errors with Dates

I'm having issues with the dates. For example, on June 6, I see the end date being June 9 in my overdue detail panel, but I configured it as June 12. When I go to edit the date, it is in fact June 12. I had to select June 12 again and save it to change.

I believe that some of my dates have inadvertently changed; it might also be a bug, but I'm not sure yet.