Thanks for bringing this to our attention. Interesting they consider it a bug. Why should any card be playable by another player within 24 hours of being played by a different player?
I find the last played flag to be not totally reliable sometimes it is on and sometimes it is not on a card I know I played.
I do generally rent out my gold foil cards for end of season due to the great bounce in prices. I would think that part of the reason ranked battle rewards are higher on the day after EOS is that everyone is waiting on the cards to be released from being rented.
!PIZZA
I think it's a bug because it's encouraged to rent out the cards through the rental market so the DEC gets burned properly? Delegations sort of circumvent that so that's why there's a 24 hour penalty there.
Those who take advantage of the system by using the same cards on multiple accounts will at least have to wait for the 24hrs of rental to expire before they can move the cards to another account.
There already is a current system for the delegation of cards. The issue at hand is that this wasn't applied to the rental system. I think that's where the code issue happened