Clearly redraw messages are not being correctly processed for the buttons in the dialog concerned.

Using the Microsoft tool SPYXX.EXE, the messages sent to the child window when the main window is tweaked when the buttons are invisible after which the buttons become visible are:

<00001> 000303B6 S WM_NCPAINT hrgn:00000001
<00002> 000303B6 R WM_NCPAINT
<00003> 000303B6 S WM_ERASEBKGND hdc:23010C57
<00004> 000303B6 S .WM_CTLCOLORDLG hdcDlg:23010C57 hwndDlg:000303B6
<00005> 000303B6 R .WM_CTLCOLORDLG hBrush:01100059
<00006> 000303B6 R WM_ERASEBKGND fErased:True
<00007> 000303B6 S .WM_PAINT hdc:00000000
<00008> 000303B6 R .WM_PAINT
<00009> 000303B6 S ..WM_CTLCOLORBTN hdcButton:7E01054E hwndButton:000303B0
<00010> 000303B6 R ..WM_CTLCOLORBTN hBrush:01100059
<00011> 000303B6 S ..WM_CTLCOLORBTN hdcButton:7E01054E hwndButton:000303B2
<00012> 000303B6 R ..WM_CTLCOLORBTN hBrush:01100059
<00013> 000303B6 S .WM_NCPAINT hrgn:00000001
<00014> 000303B6 R .WM_NCPAINT
<00015> 000303B6 S .WM_ERASEBKGND hdc:7E01054E
<00016> 000303B6 S ..WM_CTLCOLORDLG hdcDlg:7E01054E hwndDlg:000303B6
<00017> 000303B6 R ..WM_CTLCOLORDLG hBrush:01100059
<00018> 000303B6 R .WM_ERASEBKGND fErased:True
<00019> 000303B6 S .WM_PAINT hdc:00000000
<00020> 000303B6 R .WM_PAINT
<00021> 000303B6 S ..WM_CTLCOLORBTN hdcButton:7E01054E hwndButton:000303B0
<00022> 000303B6 R ..WM_CTLCOLORBTN hBrush:01100059
<00023> 000303B6 S ..WM_CTLCOLORBTN hdcButton:7E01054E hwndButton:000303B2
<00024> 000303B6 R ..WM_CTLCOLORBTN hBrush:01100059
<00025> 000303B6 S .WM_NCPAINT hrgn:00000001
<00026> 000303B6 R .WM_NCPAINT
<00027> 000303B6 S .WM_ERASEBKGND hdc:23010C57
<00028> 000303B6 S ..WM_CTLCOLORDLG hdcDlg:23010C57 hwndDlg:000303B6
<00029> 000303B6 R ..WM_CTLCOLORDLG hBrush:01100059
<00030> 000303B6 R .WM_ERASEBKGND fErased:True
<00031> 000303B6 S .WM_PAINT hdc:00000000
<00032> 000303B6 R .WM_PAINT
<00033> 000303B6 S ..WM_CTLCOLORBTN hdcButton:C4010746 hwndButton:000303B0
<00034> 000303B6 R ..WM_CTLCOLORBTN hBrush:01100059

00303B6 is the handle to the dialog frame
00303B0 and 00303B2 are the handles of the two buttons that are redrawn.

Hope this helps!

P.S. you omitted RESOURE.FD from your zipped archive which caused a lot of extra work to get your code compiled..

I played around with your MainWndProc. It looked to me that some messages were not being properly passed on, so I added calls to
DefWinowProc instead of setting MainWndProc=0 or 1. The buttons now appear,although of course,there may be other effects that your stripped-down code may not show. Here are my changes:

    select case(mesg)
                
    case (WM_PAINT)  ! Set to WM_SIZE to help with debugging

        MainWndProc = DefWindowProc( hWnd, mesg, wParam, lParam )
        return
        
    case (WM_GETICON, WM_ACTIVATEAPP, WM_NCCREATE:WM_NCMBUTTONDBLCLK)
        MainWndProc = DefWindowProc( hWnd, mesg, wParam, lParam )
        return
    end select
        
    ! Handle all events not processed
    select case ( mesg )

    case (WM_DESTROY)
        
        call PostQuitMessage( 0 )
        
    case (WM_CREATE)
        
        if (exit_buttons_dlg%hWnd == 0) then
            call CreateChildDialog(hwnd)
            call ResizeChildDialog(hwnd)
        end if          

        MainWndProc = DefWindowProc( hWnd, mesg, wParam, lParam )
        return
          
    ! Let the default window proc handle all other messages
      case default
          MainWndProc = DefWindowProc( hWnd, mesg, wParam, lParam )

      end select