WPF firing MouseDown events from incorrect locations when using touchscreen in .NET after 4.5.0

So through 4.5.0 we just let .NET touch events trickle down to regular mouse events and everything is fine.  But, .NET 4.5.1 changed something and broke this for us.

I have a datagrid, and there is no click event for WPF datagrid.  So we are using the mousedown event.  The event handler essentially does this right now:

        private void myDataGrid_MouseDown(object sender, System.Windows.Input.MouseEventArgs e)
        {
            MessageBox.Show("Stylus: " + e.StylusDevice.GetPosition(myDataGrid));
        }

The first event is fine.  Then when I touch anywhere else on the screen, the event handler still fires.  Even though the pop-up shows negative values, meaning that the event is clearly happening outside of the datagrid.

MouseDownEvent Description From MSDN: "Occurs when any mouse button is pressed while the pointer is over this element."  Clearly this is not being fulfilled by my described behavior.

Now I do have a workaround that will totally work.  But I don't want to hack my code up to support a bug in the framework.  If I explicitly handle TouchDown, StylusDown and MouseDown, the problem totally goes away.