QwtPlotZoomer- problem with zoom out

[GG2013]

Hallo,
Though there's been post previously on more or less similar issue I can't figure out my problem. Any help would be great.

In my plot I could use zoom-in perfectly okay using left mouse button. But while using right-button to zoom out there is some problem.
Say, I zoom 2 times: org->stage 1->stage 2. Then on right click once it gets back to stage 1. But when I right click again the plot vanishes, and
the y-axis scale shows 0-1000. Irrespective of how many times it was zoomed, the last click (right) always shows the same (i.e no plot & 0-1000 scale).

class Zoomer: public QwtPlotZoomer
{
public:
    Zoomer( int xAxis, int yAxis, QWidget *canvas ):
          QwtPlotZoomer( xAxis, yAxis, canvas )
    {
        setRubberBandPen( QColor( Qt::darkGreen ) );
        setTrackerMode( QwtPlotPicker::AlwaysOn ); 
 
        setMousePattern( QwtEventPattern::MouseSelect2,
            Qt::RightButton, Qt::ControlModifier );
        setMousePattern( QwtEventPattern::MouseSelect3,
            Qt::RightButton );
    }
...
};

class Zoomer: public QwtPlotZoomer
{
public:
    Zoomer( int xAxis, int yAxis, QWidget *canvas ):
          QwtPlotZoomer( xAxis, yAxis, canvas )
    {
        setRubberBandPen( QColor( Qt::darkGreen ) );
        setTrackerMode( QwtPlotPicker::AlwaysOn ); 

        setMousePattern( QwtEventPattern::MouseSelect2,
            Qt::RightButton, Qt::ControlModifier );
        setMousePattern( QwtEventPattern::MouseSelect3,
            Qt::RightButton );
    }
...
};

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