Mdi Child Form Location

I had an desktop application which uses MDIForm.In that application all the child formes are in maximized state.When i am open any form and minimized,then that child form gets minimized and no problem for for the first time.Then i have to maximize and minimize the same form then there is an automatic vertical scroll appears on MDI Form.And also the location of child form goes downwards.Similar Problem happends for other forms also.