Bad positioning of objects
Using a A4 document and millimeters as dimensions, object positioning is not really accurate. Moving an object is only possible with increments of 0.01 mm.
So for more complex objects exact positioning is not posssible.
rectifying above, 0.01 mm should be 0.05mm!!
Also on max zoom level, still 0,05 mm increment
AdminNitish Agarwal (Illustrator on Web/iPad Team) (Lead Software Engineer, Adobe Illustrator) commented
This is dependent upon the zoom level. If you are at higher zoom level you get better precision.