Hello Yusi,

The provided information and project are greatly appreciated. I confirm it is an issue. Here is the feedback item for your reference. I have also updated your Telerik Points.

To work around this I can suggest you to select each page programmatically in the Load event of the form оr just set the RadTextBox1.Text property to String.Empty instead of Nothing. Please refer to the following code snippet:

Private Sub RadButton2_Click(sender As Object, e As EventArgs) Handles RadButton2.Click
        RadPageView1.SelectedPage = RadPageViewPage2
        RadTextBox1.Text = String.Empty
    End Sub
    'or
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.RadPageView1.SelectedPage = RadPageViewPage2
        Me.RadPageView1.SelectedPage = RadPageViewPage1
    End Sub

I hope this helps. If you have any other questions do not hesitate to contact us.

Regards,
Nadya
Progress Telerik