In Claris CAD, the arrow (cursor) keys will move an object one grid division (or multiple of) or one screen pixel depending on resolution. With a ruler setting of .125" = 1' and 8 divisions/foot, it is not possible on a 72 dpi monitor at 100% to move in .125' divisions. It moves the object a multiple of the division; in this case twice the division - .25'. At 200% the resolution is doubled and therefore it is possible to move at .125' division increments. The same results will occur with a 1" = 1" ruler. If you change the zoom from 25% to 12.5% the increments will change from .125" to .25" because an .125" increment cannot be displayed.
The best way to move objects is with the location bar or the info window.