In Build 10549, Microsoft has made improvements to the Messaging app, expanded support for emojis, and opened up Cortana to users in Japan, Australia and Canada. Microsoft also no longer removes the Lumia Camera app on the Lumia 1020 smartphone. However, if you have already lost the Lumia Camera app from a previous update to a Windows 10 Mobile Insider Preview build, Microsoft suggests that you use downgrade to Windows Phone 8.1 to recover the app, the move forward with the Windows 10 Mobile update.
So what’s the huge caveat that we mentioned in the title? Well, according to Microsoft’s Gabe Aul, internal testing showed that a major, last minute bug was discovered that affected Lumia devices upgrading from Build 10536 to Build 10549. So rather than make testers wait even longer for a new build — Build 10536 was released nearly a month ago — it decided to go ahead and release it anyway.
However, in order to update to Build 10549, Microsoft is requiring that testers use the Windows Device Recovery Tool to downgrade to Windows Phone 8.1. From there you will need to install the Windows Insider app, select Fast ring, and then begin downloading Build 10549.
In the mean time, Microsoft is going to squash this bug — which cause devices to become stricken with a black screen after the OS update is completed — in future builds of the Windows 10 Mobile Insider Preview so that the back and forth downgrade/upgrade workaround is no longer necessary.