The AI protected a sundial in a T50 game (okay, that should be fixed, too, but it's not exactly a bug), and then when the sundial was gone the mark of immortality stayed behind. Later it played a golden hourglass in that same spot, and the immortality mark STILL stayed. Seeing as I run a fire/light deck with to permanent control, I have no idea if the immortality mark still had effect.
But it's still a minor graphics bug >_>.