VB.NET在父窗体调用子窗体的时候,子窗体不显示也没有错误提示

在父窗体调用子窗体的时候,子窗体不显示也没有错误提示
Module Module1
Public mT1 As T1

Public mT2 As T2
Sub subT2()
    Try

        mT1 = New T1
        mT2 = New T2
        mT2.MdiParent = mT1
        mT2.Show()
    Catch ex As Exception
        MessageBox.Show(ex.ToString)
    End Try

End Sub

End Module

下面是主窗体菜单调用的程序
Private Sub T2_Click(sender As Object, e As EventArgs) Handles T2.Click
subT2()
End Sub

但当我直接在父窗体中调用,将mT2.MdiParent = mT1 改成mT2.MdiParent = me 就没有问题