Microsoft has released the Windows 10 Mobile preview build 10549 to members of the Windows Insider team. It has also published a list of what's been fixed compared to the earlier build and what known issues are still in this new build.

Windows Insider head Gabriel Aul posted the list of the fixed problems in build 10549:

The Windows Camera app no longer crashes when certain applications launch it to capture a picture.

We fixed an issue where the touch keyboard would get dismissed every time you sent a message, which made sending 2+ texts in quick succession difficult.

We fixed an issue where swiping away a notification was causing the notification icon to appear top of your screen.

Screenshots were not being properly saved resulting in many top social messenger apps such as WeChat, WhatsApp, LINE, WeiBo, and QQ unable to find saved screenshots. This has been fixed.

We fixed an issue where you couldn't cannot launch apps saved on SD cards after reinserting your SD card.

Pinch to zoom should work properly in the Maps app now.

We fixed an issue where trying to set a custom ring or text tone for a contact shows a black screen for 10 seconds, then does nothing.

We have added back vibrate-only alarms.

We have fixed call-blocking.

There's also a short list of known issues:

After upgrade, you might be missing a few apps. If you experience this, the workaround is to reset your phone.

After rebooting your phone, you won't see notifications, such as new messages, until you unlock your phone for the first time. After that, you should see notifications for new messages just fine. This bug is fixed in a later build.

You will be unable to make calls with Skype for Business, WhatsApp and other apps after upgrading to this build. The workaround is to uninstall and reinstall these apps from the Store.

Of course, the biggest known issue with this build is that people who have the previous 10536 build will have to downgrade back to Windows Phone 8.1 in order to get the new build 10549.

Source: Microsoft