in my own testing "NTK_CENTERWINDOW" is resizing the window: the width and height of the window was being extended i.e. as compared to the width and height of the displayed window if you comment out the call to NTK_CENTERWINDOW
i wrote my own method using the NTK "GETWINDOWRECT" and "MOVEWINDOW" methods and this works fine i.e. centers the window without changing its width / height:
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Function CenterWindow(hWnd, hWndParent)
local aPos local aParentRect := NTK_GETWINDOWRECT(hWndParent) local aRect := NTK_GETWINDOWRECT(hWnd) local nHeight local nWidth