In a vertical panel, the width of the applet (not the m_Width value) does not correspond to the size of the m_History component because it is the height of the applet which corresponds to the size of that component.

So, in a vertical panel, if the width of the applet is greater than the height, there are weird lines at the left of the displayed rectangle.

With the proposed patch, in a vertical panel, the size of the m_History component corresponds to the width of the applet, more precisely, to the width of the m_DrawArea component + 1.