[2.7.0-1 wxMac] Problems (bug?) with wxScrolledWindow

[H]

When I add the following statement to the MyFrame constructor (last 
lines of the constructor) in the minimal sample I do not get a scrolled 
window with scrollbars:

    wxScrolledWindow* Ptr1(new 
wxScrolledWindow(this,wxID_ANY,wxDefaultPosition,wxSize(50,50),wxScrolled
WindowStyle | wxALWAYS_SHOW_SB));

If I add these lines to the constructor

    wxScrolledWindow* Ptr1(new 
wxScrolledWindow(this,wxID_ANY,wxDefaultPosition,wxSize(50,50),wxScrolled
WindowStyle | wxALWAYS_SHOW_SB));
    Ptr1->Hide();

    wxScrolledWindow* Ptr2(new 
wxScrolledWindow(this,wxID_ANY,wxDefaultPosition,wxSize(100,100),wxScroll
edWindowStyle | wxALWAYS_SHOW_SB));

I can see the scrollbars.

If I add another line:

    wxScrolledWindow* Ptr1(new 
wxScrolledWindow(this,wxID_ANY,wxDefaultPosition,wxSize(50,50),wxScrolled
WindowStyle | wxALWAYS_SHOW_SB));
    Ptr1->Hide();

    wxScrolledWindow* Ptr2(new 
wxScrolledWindow(this,wxID_ANY,wxDefaultPosition,wxSize(100,100),wxScroll
edWindowStyle | wxALWAYS_SHOW_SB));
    Ptr2->SetSize(200,200);

Then, the scrollbars are gone again. It seems to be that the SetSize 
method lets the scrollbars disappear. Why I do not know because I am not 
so familiar with the Mac interface routines.
In the very first example SetSize is not explicitely called but I guess 
implicitely.

Any ideas?

Hartwig