Android Question Strange behavior of Canvas

#Region  Project Attributes
    #ApplicationLabel: B4A Example
    #VersionCode: 1
    #VersionName:
    'SupportedOrientations possible values: unspecified, landscape or portrait.
    #SupportedOrientations: unspecified
    #CanInstallToExternalStorage: False
#End Region

#Region  Activity Attributes
    #FullScreen: False
    #IncludeTitle: True
#End Region

Sub Process_Globals

End Sub

Sub Globals
    Private imvForeground As ImageView
End Sub

Sub Activity_Create(FirstTime As Boolean)
    Dim cvs As Canvas
    Dim img As Bitmap
    Dim Rect1 As Rect
    Dim Rect2 As Rect

    Activity.LoadLayout("Main")

    cvs.Initialize(imvForeground)
    img.Initialize(File.DirAssets, "image.png")
    Rect1.Initialize(0, 0, img.Width, img.Height/2)
    Rect2.Initialize(0, 0, img.Width, img.Height/2)
    cvs.DrawBitmap(img, Rect2, Rect1)
    imvForeground.Invalidate2(Rect1)
End Sub

Sub Activity_Resume

End Sub

Sub Activity_Pause (UserClosed As Boolean)

End Sub