Related su Demai 4:11

The terumah of tithes of demai (doubtfully tithed produced) that fell back into their [former] place creates a forbidden mixture [of tithed and untithed produce], [but if it fell into] a different place, it does not create a forbidden mixture, the words of Rabbi Eliezer. And the Sages say, whether in its [former] place or in a different place it creates a forbidden mixture. Rabbi Shimon says, whether in its [former] place or in a different place, it does not create a forbidden mixture.