A debian user reported that having the window size automatically calculated leaded to some resizes before xfce4-about is fully started, and that on slow computers it was not really beautiful. More details can be found in original bug report (details about licenses text box too small and about operation order, resize-draw or draw-resize).
Erf, sorry, didn't search enough for dupes. *** This bug has been marked as a duplicate of bug 3806 ***