I'm here to put my two cents in and say yet the same thing.
I have resorted to keeping the remaining backup disk pieces in the cash shop warehouse, as I have lots about 8 pieces total from the my personal warehouse.
I have collected one every day, and yet I have none to show for it (save for the ones in my CS Warehouse). I am hoping someone does look into this, as it's very annoying to be given an item for an event, and have it taken away.
Please look into this, and everyone else out there, keep posting to bump this up.
Thanks for hearing me out!