פירוש על קידושין 111:1

Second tithe money should not be used to buy food outside of Jerusalem. According to the first opinion, if one uses second tithe money to buy an animal outside of Jerusalem, if unwittingly, the sale is void. The money returns to its “place” meaning it stays second tithe. But if he does so deliberately, the sale is valid and the animal must be brought to Jerusalem and eaten there.
R. Yehudah explains the first opinion—the person was buying an animal to be used as a peace-offering, which seems to have been a normal thing to be done with second tithe money. If he does so intentionally, then the acquisition is valid. But if he was trying to buy a non-sacred animal, meaning his intent was to turn the second tithe into non-sacred money, then the exchange is invalid whether done unwittingly or deliberately.