After updating the client and changing my Bo1 decklist with Teferi, Hero of Dominaria to include Dovin's Veto, upon saving the decklist I receive the message, "Teferi, Hero of Dominaria requires the deck to have a sideboard". As far as I can tell, I can still run the list in Bo1 currently. I'm hoping this is a bug and not an accidental leak of an upcoming Bo1 ban for Teferi?
This is a bug; that message is intended for cards like [[Mastermind’s Acquisition]], but it looks like Teferi is inadvertently triggering it too. Thanks for the report.