Ahead of the Lumia 950 hitting shelves, Microsoft has been forced to remove a feature from Windows 10 on mobiles that was causing an app to constantly crash. The Mail and Calendar app last week received an update that introduced a unified inbox. That didn't work properly, however, and Windows Central reports that Microsoft has backtracked by removing the feature altogether in a further update.

The unified inbox was intended to provide a single screen of all the emails in every inbox. It has been a staple of the iPhone since iOS 4 in 2010. The removal of the feature will be a blow for customers expecting the new Lumia to stack up well against the competition.

Windows needs all the help it can get on mobile. Gartner's third-quarter 2015 report revealed the system shipped on only 1.7 percent of phones globally, compared with 3 percent in the same quarter last year. 

The Lumia 950 and its bigger brother the 950 XL represent a major push to make Windows 10 an operating system that runs on all devices. Microsoft will need to demonstrate to hardware partners and developers that the platform is worth investing time in while keeping bugs to a minimum.