Text disappear on the TextBox on the DataRepeater

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VB

Hi everyone,

When I Dragged a DataRepeater into my form. Added a TextBox to the DataRepeaterItem. Then Added A button to the form. Write such code:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    DataRepeater1.VirtualMode = True
    DataRepeater1.AddNew()
End Sub

Then run the project,do the following steps:

Press Add Button
input into textBox "1"

Press Add Button
input into textBox "2"

Press Add Button
input into textBox "3"

Press Add Button
input into textBox "4"

Till Here Every Thing is Fine.

Then Scroll data repeater Up, "1" disappear.
Does anyone know why this happen? How can I prevent? Thanks for any suggestions.

Best regards