Vibrating item frames at distance far from spawn

I made a map for my server where I set up my base at x=1000000 y=128 z=0. We haven't noticed any problems at all, though picture frames seem to vibrate with motion and become stationary again when stopping. I did some experimentation, and this problem seems to not exist at x=0 z=0 and the motion is far more severe at x=20000000 z=0. Item frames can't even be placed at x=25000000 z=0.