When RadMessageBox has not owner and it is using in form that has TopMost = true throws exception after first call of RadMessageBox.Show()

Steps to reproduce:

1.Create From with TopMost  = true

2. Add button and insert the following code in press event:
RadMessageBox.Show("Text");
3.Run application and press the button two times.

Workaround after each show of RadMessageBox add this code snippet:
RadMessageBox.Instance.Dispose();