Microsoft released a new Windows 10 Mobile preview today. There are no new features in this new build for phones, but the upgrade bug has finally been fixed.

For many builds now, Windows 10 Mobile has had an annoying bug that prevented upgrades from earlier builds. As a result, testers had to flash Windows Phone 8.1 back onto their devices before upgrading to builds 10549 or 10572. Today’s build finally allows you to upgrade directly. Microsoft is purposefully releasing this build with only fixes and “general performance improvements” so that it can get most of its testers onto the latest and greatest.

In addition to the upgrade bug, this build also fixes the following issues:

  • For devices upgraded from Windows Phone 8.1 like the Lumia 930, Lumia Icon, and Lumia 1520 that had the “Hey Cortana” feature – with this build “Hey Cortana” should work again in Windows 10. To make sure it’s turned on, just go to Settings > Extras > Hey Cortana.
  • You can now select photos for sharing through third party apps like Facebook, Facebook Messenger, Instagram Beta, WhatsApp, etc.
  • Battery life should be improved in this build as several bugs impacting battery life have been fixed.
  • An issue where you couldn’t choose some apps to show quick status on the Lock screen via Settings > Personalization > Lock screen has been addressed.
  • Improvements to text prediction and auto-correction.
  • Video recording functionality has been improved.
  • Visual Voicemail sync should now work properly.
  • The dual-SIM issues that appeared in Build 10572 have been fixed.
  • The issue found with Build 10572 where the Chinese Pinyin QWERTY keyboard stopped working after upgrading from Windows Phone 8.1 has been fixed.

Today’s update bumps the Windows 10 build number from 10572, made available to testers on October 20, to build 10581. Unlike Windows 10 for PCs, which launched on July 29, Windows 10 Mobile hasn’t been released yet — it’s behind in terms of features and polish compared to its PC counterpart.

Build 10581 has the following known issues:

  • As with previous builds, after applying this update the device may appear at a black screen for about 5 minutes when transition between the spinning gears and the final stages of update. Just be patient and it should progress past it. Exact time will vary by device.
  • You will be unable to set your default save locations via Settings > System > Storage and will not correctly reflect the current storage settings. If you are using a SD card in your phone, it will show up as a garbled name in Storage settings. Whatever you had configured for your save locations in the previous build will be the same.
  • After moving some apps to a SD card, those apps might crash. The workaround is to reboot your phone and those apps should work fine thereafter.
  • Deploying Silverlight apps through Visual Studio to your phone won’t work in this build. You can deploy UWP apps to your phone without any issues.
  • If you restore a backup from a phone that had a different resolution, you may end up with a corrupted Start experience. The workaround is to go to Action Center (which won’t be corrupted), then Settings > Personalization > Start and apply a different background picture.

Microsoft plans to launch the first Windows 10 phones in November and roll out Windows 10 Mobile to existing Windows Phone users in December.