Created attachment 15602 [details]
Solution reproducing the problem.

Given the following page layout for an application:

            AbsoluteLayout mainLayout = new AbsoluteLayout()
            {
                BackgroundColor = Color.White
            };

            MainPage = new ContentPage
            {
                Content = mainLayout
            };

            BoxView view = new BoxView()
            {
                Color = Color.Black
            };
            mainLayout.Children.Add(view, new Rectangle(0, 0, 1, 1), AbsoluteLayoutFlags.All);

An approximately 1px border of white will be shown behind the BoxView, as the bounds for the BoxView are not calculated correctly for some devices.  The issue appears to be related to fractional "logical" bounds for the viewport, as devices which yield a whole number for Width and Height do not exhibit the problem, while those that have fractional bounds do.  For example, the Nexus 5 with a resolution of (1080 x 1776) and a density factor of 3 yields logical bounds of (360 x 592) and does **not** exhibit the problem, while the Nexus 6 with resolution of (1440 x 2392) and a density factor of 3.5 yields logical bounds of (411.42857143 x 683.42857143) and **does** exhibit the problem.

It would appear then that the problem is related to an integer truncation somewhere since instead of using:

mainLayout.Children.Add(view, new Rectangle(0, 0, 1, 1), AbsoluteLayoutFlags.All);

on the Nexus 6, I can use:

mainLayout.Children.Add(view, new Rectangle(0, 0, 411.42857143, 683.42857143), AbsoluteLayoutFlags.PositionProportional);

and the problem will **not** occur.

Attached is a solution reproducing the problem.