The copies stay in your hand untill your next turn, seems like a bug?
I assumed it would act like HUF where the added spells are played as part of the current stack…
Check the bugs thread, there is a long conversation going on about that very card.
Apparently it is intentional that you must wait a turn before casting the copy.
And, like most things, to make people not think it’s a bug it needs to be written on the card…