Can someone please tell me why, when I enter 04/18 into Textbox10 as soon as I go to TextBox11, TextBox10 changes to 04/16

Like its set to automatically only display this year! grrr

Private Sub TextBox10_Exit(ByVal Cancel As MSForms.ReturnBoolean)
    TextBox10.Text = Format(TextBox10.Value, "mm/yy")
End Sub