Actually, i've noticed this with my fighterstick too. When i had it apart a whiles ago, i noticed why it does it. Its in the gimble design itself. Its kind of a clam-shell sort of set-up with two springs per axis - on for up, one for down, with each one returning to the centered home position. When you pull it apart, you'll see what i mean. Hard to describe. I dont think its the pots.
Mine does do this but only very very slightly, and a small dead-band setting dials it out totally.
I wondered if putting stronger tension springs on the gimbles would reduce this issue?