Something not right when window is displayed with dynamic caption.

I have following code which enables/disables caption on key:

Me.ControlBox = Not Me.ControlBox

If Me.ControlBox Then

Me.FormBorderStyle = Windows.Forms.FormBorderStyle.Sizable

Else

Me.FormBorderStyle = Windows.Forms.FormBorderStyle.None

End If

Initially window is shown without caption and occupies full screen. 
Everything is OK.



When caption is displayed and then removed with this code, there is small 
arefact left on screen - part of caption to the right of last control button 
and screen area expanding below it. If there was bitmap overlapping this 
area, you can see remaining pixels. New bitmap is shown under this area 
(it's painted over new bitmap). Invalidate/Update doesn't change this.



Seemingly eigther I do something wrong, or .Net 2.0 painter. Could this be 
corrected and how?

Alex