Steps to reproduce:
1. Add a new form to a project and set MdiContainer to true
2. Drag a RadDock onto the form and set the AutoDetectMdiChildren to true
3. Add another form to be used as MdiChild
4. Drag a button onto the second form and in the Click event handler add call to this.Close()
5. Run the project and add an MdiChild form to the MdiContainer form.
6. Press the button on the child form. You will see an exception.