Unfortunately, I didn't catch the game number and server (there doesn't seem to be a way to check past games), but it happened today (as of posting this) just about 5 minutes ago.
Anyway, I have a screenshot of it. My opponent plays Rebuild and accidentally clicks estate. They only have estates and ask for a redo, so I oblige. After the redo, no victory card is trashed, but they gain a Duchy somehow. According to them, on their client, they trashed an Estate and got a Duchy. I don't see their estate in the trash, but the log has them gaining a Duchy. On my next turn, I play a Rebuild and trash my own Duchy to get a Province. Then I play the second Rebuild you can see in the picture and trash an Estate. However, the game will not allow me to get a Duchy! It only lets me get an Estate. I tell my opponent and ask for an undo. My opponent grants it, and everything seems to be fixed. The log (turn 13, opponent's turn) is fixed and their Estate appears to be trashed in it, the Estate shows up in the Trash, and when I play Rebuild again after my undo, I can gain a Duchy after trashing an Estate, so the game state seems to have figured itself out. Seems like a weird desync error.
In conclusion, as you can see in the screenshot, turn 13, my opponent Rebuilds and just gains a Duchy but on their screen they say the Estate is trashed. Later on my turn, I cannot gain a Duchy when I trash an Estate until I ask for an undo. After the undo, the log is fixed and the game state seems to go back to normal, and I can gain a Duchy after trashing an Estate.