I’m not sure if it’s just the animation or not but when I cast Day’s Undoing, I only see the new 5 cards at the start of my next turn. If it’s just the visuals it’s not a big deal but if it’s the effect too then it matters cause of stuff like Liliana’s ability and Sphinx Tutelage.
One of the times I casted it, the spell also did not discard the opponent’s hand, allowing the opponent to summon his (nearly full mana) creature the next turn.
I think it’s just a display bug, but it’s definitely an issue. You need to be able to re-arrange your hand and exile cards from your hand when you draw a fresh hand an get to go again because of a match 5.
Thanks for posting those. I should have noticed. Anyway I confirm that it doesn’t work immediately as it should. I just played Day’s Undoing and got a free turn from a match-5. I still only have my old hand to work with.
edit
After playing a few more rounds with DU, I’ve noticed it works in some matches but the glitch happens in other matches. So it’s not 100% repeatable.
The glitch is there most of the time but, functionally, the card is working. The problem, as you mentioned, is when you match-5 to cast DU and can’t access your cards to reorder them.