I may be wrong and this isn’t a bug, but the pets change size depending on the player’s size. If I drink a tiny potion then press K, when I spawn, the pets are tiny with me. Opposite effect with large potion. Also, pet size stays after you remove potion (take off tiny potion after respawning, pets stay tiny until you press K again while a different size).
EDIT: You can use a potion, unequip a pet, then reequip the pet for the same result.
Tiny pets (in this one, after I respawned in, I took off the potion)