用VB.net里的Timer控件动态生成随机数，在点击Button2停止Timer控件时，在软件界面中的三个Label会有跳码的现象，很不解，为此，我在网上找了一段截屏的程序在对每次停止Timer控件时，截取屏幕的图，进行对比，发现截屏后，三个Label控件显示的值与软件界面上显示的三个Label的值有时不一致，有时一致的现象，请问各位高手，这是怎么回事呢？
附代码：

Public Class Form1



    Private Sub CatchLDDRezult()

        Dim p1 As New Point(0, 0)

        Dim p2 As New Point(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height)

        Dim pic As New Bitmap(p2.X, p2.Y)

        Using g As Graphics = Graphics.FromImage(pic)

            g.CopyFromScreen(p1, p1, p2)

            pic.Save("D:\1.jpg")

        End Using

    End Sub



    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load



    End Sub



    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Timer1.Enabled = True

    End Sub



    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click

        Timer1.Enabled = False

        CatchLDDRezult()

    End Sub



    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick

        Randomize()

        Dim intRndLDid As Integer = Int(Rnd() * 941 + 1)

        Dim strRndLDid As String = Format(intRndLDid, "0000")

        Label1.Text = strRndLDid



        Randomize()

        intRndLDid = Int(Rnd() * 941 + 1)

        strRndLDid = Format(intRndLDid, "0000")

        Label2.Text = strRndLDid



        Randomize()

        intRndLDid = Int(Rnd() * 941 + 1)

        strRndLDid = Format(intRndLDid, "0000")

        Label3.Text = strRndLDid



        Label4.Text = Now

    End Sub

End Class