Game #10027983, my opponent had requested an undo after playing a Cartographer (I don't remember specifically when the undo was requested), I accepted it, then the log messed up with what was shown for Menagerie:
Turn 12 - rainshifter
r plays a Menagerie.
r reveals 3 Coppers, an Apothecary, an Estate, a Silver and a Gold. <--- too many cards revealed here
r draws 3 cards.
r plays a Cartographer.
r draws a card.
r looks at 4 cards.
r topdecks 4 cards.
I know that too many cards were revealed because I remember my opponent having 7 cards in hand when playing the Cartographer.
Thanks for reporting this! I'm pretty sure it is the same problem that others and I have previously found when reloading a game (which AFAIK uses the same infrastructure as undoing). What happens is that the log will now list the current contents of the players hand (for Menagerie), instead of the contents at the time when it happened. So you got to see what your opponent had in hand after the Menagerie (if that is the point to which the undo happened).
yes thanks for reporting... this is a lot worse then I realized and I fixed it today (so it will be in the next release).