shaped sub-form inside mdicontainer

[sambo]

I have a parent form that houses multiple sub-forms. I have set the TransparencyKey of the sub-form to {128,255,128}. Then I created a bitmap image that will be used as the BackGroundImage of the sub-form. I filled the exterior of the image with {128,255,128}. This should give the shaped subform effect.

If I create the sub-form stand alone, then I get the desired effect and the sub-form is shaped.

Application.Run(new frmSubForm());

However, if I run the mdiform and then create a sub-form inside of the parent, the sub-form is no longer shaped.

Application.Run(new frmMdiContainer());

How do I make the sub-form appear as a shaped form inside of the mdicotainer form?

I referenced this article... http://www.codeproject.com/dotnet/GraphicalForms.asp