Weird!!
I assumed it worked when I got the order, but I tried to place them on top of each other and it didn't work for me, so I was like "of course, two of the same can't go on top of each other".
oooh I see!! I didn't undertstand your problem at first sorry. Yeaaah you can't place ashes on top of ashes as you said it, but there's a way to achieve it! hint below: (and thank you for your kind comments!)
hint: as you can't place ashes on ashes, perhaps you will need to place the two cards on each other before they become ashes