I got the impression that Rumple had a break in or something and that is when he noticed that the ingredients were missing. I do think this is Regina’s intended curse to use and not Rumple’s.
It looked like Mr. Gold and David were in Regina’s heart vault when they found Mr. Gold’s bag. So either Regina broke into his pawn and took his bag of magic potions back to her vault, or Mr. Gold gave her the bag and then asked David to help him find it so to make it appear like Regina had stolen it.
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"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy