The first is the possibility of having three Pikmin carry a single one-weight pellet. In some rare cases, when one Pikmin attacks the leaf of a Pellet Posy, and two are attacking it from the ground, they will all carry the pellet. The second is the chance of having the sides of a large pellet point up and the Pikmin carrying it will appear to be standing in mid-air while holding it. They'll bring it back to the Onion normally. Simply call them back and order them to pick it up again to fix it. This also happens with some such as the Libra. Pellets can also cause the Crushing glitch.