To reproduce:
- set the Mask to P2
- set the MaskType to Numeric
- set the control value to 0.024

The the control displays "2.4" instead of "2.4 %"

WORKAROUND: 
  Private Sub RadMaskedEditBox1_ValueChanged(sender As Object, e As EventArgs)
        Dim control As RadMaskedEditBox = DirectCast(sender, RadMaskedEditBox)
        RemoveHandler control.ValueChanged, AddressOf RadMaskedEditBox1_ValueChanged
        control.MaskedEditBoxElement.TextBoxItem.Text = control.MaskedEditBoxElement.Provider.ToString(False, True)
        AddHandler control.ValueChanged, AddressOf RadMaskedEditBox1_ValueChanged
    End Sub