SIP disabled after showing maximized form

After showing a maximized form the SIP (InputPanel) on the calling
form (which has a MainMenu) is not displayed when tapped. Putting on a
breakpoint I notice that EnabledChanged for InputPanel1 is called 2 or
3 times with a value of 'Disabled' each time. There is no problem on
the Emulator, just on the real device. Anyone know what's
going on?

Here's the code:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim form2m As New Form2
form2m.ShowDialog()
End Sub

Private Sub InputPanel1_EnabledChanged(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles InputPanel1.EnabledChanged
If InputPanel1.Enabled Then
MsgBox("Enabled")
Else
MsgBox("Disabled")
End If
End Sub

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Me.WindowState = FormWindowState.Maximized
End Sub

TIA, Eric