Microsoft have recently pushed an update for the Calendar app on the Windows Phone 8.1 Developer Preview, demonstrating the company’s ability to push updates to core apps within the OS without having to update the entire system.
The update unfortunately (which also came with no change log) introduced a serious bug that would cause the calendar to crash to the Start screen whenever the user tries to create or edit appointments. This is true for the Windows Phone 8.1 Developer Preview and devices that shipped with 8.1 and Lumia Cyan out of the box -- like the Lumia 630.
Thankfully, Cortana can still perform all of your calendar related duties using your voice -- successfully creating, editing, and deleting appointments. While this workaround may still be inconvenient for those of you that like to manually enter your appointments, it’s the only one currently available. Microsoft is aware of the issue and should release an update to the app soon.