Noobish problems with QwtPlotPanner

Hi. The troubles are:
1) when i move the plot by mouse, it could be moved far away from any needed area. How can i tell Qwt the EXACT plotting zone?
2) when the plot is being dragged and not dropped,only the part, the previously visible part is drawn. How can it be fixed?

Code:

#include <QtGui/QApplication>
#include <QVector>
 
#include <qwt_plot.h>
#include <qwt_plot_curve.h>
#include <qwt_plot_panner.h>
 
#include <qwt_plot_grid.h>
#include <qwt_plot_canvas.h>
 
#define NUM_OF_POINTS 1000
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
 
	QwtPlot* megaPlot = new QwtPlot(QwtText("MegaPlot"));
	QwtPlotCurve* megaCurve = new QwtPlotCurve("MEGALINE");
	double x[NUM_OF_POINTS], y[NUM_OF_POINTS];
	for(int i = 0; i < NUM_OF_POINTS; i++)
	{
		x[i] = i;
		y[i] = i*i;
	}
	megaCurve->setData(x,y,NUM_OF_POINTS);
	megaCurve->attach(megaPlot);
 
	QwtPlotGrid* megaGrid = new QwtPlotGrid;
	megaGrid->enableXMin(true);
	megaGrid->enableYMin(true);
	megaGrid->attach(megaPlot);
 
	megaPlot->resize(640,480);
 
	QwtPlotPanner* megaPanner = new QwtPlotPanner(megaPlot->canvas());
	megaPanner->setMouseButton(Qt::RightButton);
 
	megaPlot->show();
	return a.exec();
}