Thank you for writing.
When you are developing a Windows Forms application and the design of your form requires several docked controls, it is important to place the controls on your form in the correct order. Otherwise, you may not get the desired result. Please refer to the following KB article which is quite useful on this topic: http://www.telerik.com/support/kb/winforms/details/docking-controls-on-a-form-in-a-windows-forms-application
I hope this information helps. Should you have further questions I would be glad to help.