As the title says, pixes can steal items directly from the player's inventory. Most recently I had one steal off my sword and chestplate right off me while I was flying and send me crashing to the ground. Other items were stolen too. I managed to recover everything, but even soul bound is not a protection against this. And I needed to kill every pixie and tear up the forest to ensure no more would spawn while I eliminated them all to get rid of them.
Unless you want items people to have random items remove I would recommend:
ice_and_fire.cfg (Ice And Fire):
# True if pixies are allowed to steal from players [default: true]
B:"Pixies Steal Items"=false