Events that have end time set to 00:00 are not visible on day, week, 5days views.
It can be replicated even on calendar demo site.
Just click on calendar and set EndDate to 00:00 hour in Create event popup and click OK. Nothing happens.
Click on Switch TimeZone and event is visible (it does not ends at 00:00 anymore). Click Switch TimeZone again and it disapears again.