I moved down one space from my initial position, and my character picked up all the items on my previous position and then dropped them down on the next tile. If I move over to other positions he will continue to amass all of the items he is picked up so far. None of the items he is trying to pick up have been toggled to be picked up automatically, and there are 8 liters of volume in my inventory leading me to believe that my character is picking them up and dropping them without checking to see if there is inventory space to deposit them.
It stopped happening once I exited and logged back in.
It sounds like the character is using the hauling function. I haven’t tried it yet, but it might be something you toggle on and I believe the default key for it is “/”. If that isn’t it, you can check the keybindings using Esc.
It’s supposed to be useful for piling up everything, especially bodies, after a fight against a large horde.