autoclear Panel.Controls ?

 Hello,
 
i have a small WebForm with 2 Buttons and 1 Panel.
Click-Event Button1:
 
Dim text1 As TextBox = New TextBox
text1.Text = Guid.NewGuid().ToString()
Me.Panel1.Controls.Add(text1)

Dim text2 As TextBox = New TextBox
text2.Text = Guid.NewGuid().ToString()
Me.Panel1.Controls.Add(text2) 
i simply add 2 Textboxes as Controls to my Panel. it works.
 
 in my second Button nothing happens there is no code... but if i click
on the button the page "reloads". And then my Textbox-Control which i added
are deletet?!
 
what is my mistace?

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