I think what's happening is that when a colonist picks a potato to eat it raw, they move 5-6 tiles away and plop down on the ground to eat. I had a hydroponics table underground, very close to an exterior wall. Multiple times I had a colonist pick some food and then attempt to move to a spot on the other side of the wall which was still within that 5-6 tile radius of the farm. This resulted in them walking a long, long way just to eat and then come back.
This kept happening over and over, and not every colonist would do it either. Some would pick spots inside to eat, some would go outside.
The easy solution was to quickly draft and undraft the colonist. They would drop the food, pick it up, then move the same 5-6 tiles from wherever they were to eat. If they were near the table and chairs in the base when I did this, they would sit there to eat.
I playing the 250 build, 64-bit Win7.
I hope that makes sense.