Internal error: pc 0x0 in read in psymtab, but not in symtab.

[kpkale]

I get this error at many places in my GUI CAD application. On searching various forums or like the thread here... http://qt-project.org/forums/viewthread/16634, I could understand that this error is because of improper memory management. The result that I have is also same, the program works in debug mode giving this error but crashes when run in release mode.
What I dont understand here in my perspective is how to do proper memory management. Following are more details about my problem.

1. The application is a CAD application where all the items being drawn on the Scene are QPainterPaths subclassed items with various other properties.
2. In discussion is a QUndoCommand which I am using for distributing the selected items "Equal Top Distance".
   The header and C Source is given here.
   The Header File:
   @#ifndef DISTRIBUTEENTITIESCMD_H
   #define DISTRIBUTEENTITIESCMD_H

#include <QUndoCommand>
#include <QWidget>
#include "linecurvepathitem.h"
#include "mymainview.h"

bool topsort(basegraphicentity* e1, basegraphicentity* e2);

class distributeentitiescmd : public QUndoCommand
{
public:
distributeentitiescmd(mymainview *thisview,int mode,QUndoCommand *parent=0);

void undo();
void redo();

private:
mymainview *myGraphview; // pointer to the graphics view.
mymainscene *myGraphscene; // pointer to the graphics scene.
int mymode; // mode of working (1 = distribute equal tops)
QList<basegraphicentity *> mylist; // This list saves the pointers of selected items in the scene.
QList<QPainterPath> myoldpath,mynewpath; // lists for saving old and new values of path.
qreal first,last,change,tempval,inchw;

};

#endif // DISTRIBUTEENTITIESCMD_H
@

The CPP File.
@#include "distributeentitiescmd.h"

distributeentitiescmd::distributeentitiescmd(mymainview *thisview, int mode, QUndoCommand *parent)
:myGraphview(thisview),myGraphscene(thisview->sceneobject),mymode(mode),
QUndoCommand(parent)
{
mylist.clear();
myoldpath.clear();
mynewpath.clear();
if(mode==1) // Distribute Top
{
foreach(QGraphicsItem *myitem,myGraphscene->selectedItems())
{
if(basegraphicentity *myGraphitem = dynamic_cast<basegraphicentity *>(myitem))
mylist.append(myGraphitem);
}
qSort(mylist.begin(),mylist.end(),topsort);
first= mylist.first()->TopLeft().y();
last = mylist.last()->TopLeft().y();
change = (last - first) / (mylist.count()-1);
for(int i = 0;i<mylist.count();++i)
{
myoldpath.append(mylist.at(i)->path());
QTransform mytrans;
tempval = mylist.at(i)->TopLeft().y();
tempval = (first + (change * i) - tempval);
mytrans.translate(0,tempval);
mynewpath.append(mytrans.map(myoldpath.at(i)));
}
}
}

void distributeentitiescmd::undo()
{
for(int i = 0;i<myoldpath.count();++i)
{
mylist.at(i)->setSelected(false);
mylist.at(i)->setPath(myoldpath.at(i));
}
myGraphscene->update();
}

void distributeentitiescmd::redo()
{
for(int i = 0;i<myoldpath.count();++i)
{
mylist.at(i)->setSelected(false);
mylist.at(i)->setPath(mynewpath.at(i));
}
myGraphscene->update();
}

bool topsort(basegraphicentity *e1, basegraphicentity *e2)
{
qreal y1=e1->TopLeft().y(),y2=e2->TopLeft().y();
return (y1<y2);
}
@

Here, If I run this routine in Debug mode, everything runs fine. however, I get this error.
Can someone suggest how to ensure proper memory management in this.