Card.delved corner case
EDIT: On closer inspection the wording of Ethereal Forager is MUCH different than Soulflayer. Soulflayer cares about the cards used to pay the cost, and then it seems anything can happen to them and it doesn't affect Soulflayer. Ethereal Forager doesn't have the "with CARDNAME's delve ability" at all, so if you could somehow get the Forager enabled to exile more cards somehow, some truly wild shenanigans could ensue.
Initial post to follow:
There are currently two MTG cards that interact with cards used to pay their Delve costs: Ethereal Forager, Soulflayer
Most notably with Ethereal Forager, if a card that was used to pay its Delve cost is later returned to the exile zone, it is still a valid option for Forager's trigger.
I believe that cards used to pay delve costs like this that leave exile and later return for a different reason should no longer be "remembered" by the host card... just not quite sure what to tweak in the java files to do this.