RE: 5855 tablet lost auto rotation
I wasn't clear enough. The issue isn't the status of the "Lock rotation on this display" slider.
That slider disappeared (along with the related "notification action" button) with the update too.
One can restored those UI items by adding: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersionAutoRotationSensorPresent=1 to the registry.
The problem is that, after the update, the tablet appears to have lost the feature of being able to "auto rotate".