In the editor if you were to move an entity for a large distance, say from <0,0,0> to <8700,0,0> you start getting decimals on your positions even with the grid snap on. You can make it occur with a shorter move if you go into the z axis. There also is almost a hard limit as to where the drifting occurs. I know for certian as you approach 8600 - 8900 in the +x axis the smaller the move is to begin drifting.