This is a documentation issue, the documentation will be updated to explain this issue at version 2.3. Prior to version 2.2, Infowindow.show accepted only screen point as arg, at 2.2 it also accepts map pointl. If you specify the map point precision is not lost on zoom. So in the problem code use graphic.geometry as the argument to Infowindow.show method instead of evt.screenPoint. For line/polygon geometry, the sample could use evt.mapPoint.