I’ve come across an interesting bug in the Admin Center Preview portal in-regards to the domain purpose changing without reason. This is further to my recent blog posting: http://realtimeuc.com/2016/06/federation-fails-with-o365/, which required disabling the Skype for Business domain purpose for domains using On-Premises or Third-Party hosted environments without hybrid configured to resolve federation issues.
You can use the Azure AD PowerShell to check domain purpose (https://msdn.microsoft.com/en-us/library/jj151815.aspx):
Now to the bug…. While using the Admin Center Preview portal, go under Settings, Domains, select your Custom domain, click DNS Management and use any option (Next/Back/Exit), you now have enabled all the domain purpose items without notification or warning.
At this point the only way to modify the domain purpose is to revert back to the old Admin portal and follow the steps outlined in http://realtimeuc.com/2016/06/federation-fails-with-o365/:
Reported to Office 365 support.