In Windows Phone 8.1 certain core services have changed in that they can be updated dynamically, bypassing the requirement for a full-fledged OS update. In theory, that should allow Microsoft to respond to the rapidly changing market by delivering faster paced, piecemeal updates. In reality, it also increases the chances that something may go wrong, and that is exactly what has happened.

Last night Microsoft pushed out a rare update for the calendar app, which was disentangled from the OS in 8.1, much like Xbox Music. The update brought the version number to 1.0.14127.246 and there was no changelog. Although it is exasperating to users to have to update an app without knowing what changed – or improved, it is even more vexing when that update breaks something.

Immediately following the update, people in comments started to complain that the attempting to create or edit an appointment caused the calendar app to crash. We have tested the update on various devices, including the Lumia 630 with the Lumia Cyan firmware, and they all have the same problem, rendering the calendar app a view-only tool.

Currently, there are over 500 comments left in the original article, most of which vouch for the instability that the update has caused.

One temporary work-around is to use Cortana, who can add appointments directly to the OS, or to use one of the many third-party calendar apps found on the Store. However, Cortana is currently a US-based system, only accessible by changing regions on the device.

Combined with the ongoing disappointment with Xbox Music, Microsoft seems to be turning allies into enemies with these snafus. Although I expect Microsoft to put out a rapid fix for the calendar, it does not sit well with the base that something as obvious as this bug went unnoticed during testing. This crash is not some rare, hard to replicate issue and frankly they should be embarrassed. Windows Phone 8.1 is just starting to be pushed out for over-the-air updates or is already being sold on devices like the Lumia 635, just announced today for T-Mobile. This screw-up is a bad headline at the wrong time.

We've reached out Microsoft for comment on the situation. Since a few hours ago, the offending calendar app has been hidden in the Store to prevent others from updating.