[wxMac 2.8x] wxWindow::DoGetBestSize bug still not solved

[H]

I already posted this a while ago but did not get an answer. Therefore, 
my next try.
This is the statement causing problems:

    else if ( !GetChildren().empty()
#ifdef __WXMAC__
              && wxHasRealChildren(this)
#endif
              )

There is also a remark related to "wxHasRealChildren" that "scrollbars 
are explicitely children" on the Mac (whatever it means).

Why is wxWindowBase::DoGetBestSize() returning wxSize(0, 0) if the 
window only has scrollbars? I thought it would at least return the size 
needed for the scrollbars.
The real problem is that some modules (example: wxTreebook) assume that 
a window's client size is zero or larger. But with this implementation 
of DoGetBestSize() this is not the case anymore, it becomes negative!
I am willing to provide a patch as long as somebody tells me what I am 
allowed to modify in wxWindow. Especially I am interested why 
wxHasRealChildren(this) is necessary at all. Baiscally, this method is 
the root of all problems in this case. This method is only used in 
DoGetBestSize as far as I can see.

Hartwig