Island Living - shells missing

My sims just spent a day in Sulani, and like every time someone go there on vacation, they do a little beachcombing to bring home a shell or two as a souvenir. This time I saw they found art least one shell, but when they got back home there were no shell in that sim's inventory... I checked their household inventory too, but nothing there. He took some pictures while on vacation, and those pictures are in his inventory.

So, what happened? In this case my sims traveled back home before they ended the vacation. Is that the reason? Will sims need to end vacation while in Sulani to keep shells?