Can't have a child window in the non-client area painting itself

[DaFrawg]

If I create a window in another window in the non-client area then send the WM_PAINT message to the child window if the parent receives a WM_NCPAINT message, the client window doesn't redraw (the non-client area it is on is still garbled with the old pixels that were in those rect). How can I solve this?