yes, I have built my code with debugging symbol and i have done a lot of in mouse event, it also crashes when zoom the view on mouse event not always.........
and when i debug, i see after doing all the stuffs at an action

here obj pointer is valid but not in scope

QObject *QMetaObject::cast(QObject *obj) const
{
if (obj) {
const QMetaObject *m = obj->metaObject();
do {
if (m == this)
return const_cast<QObject*>(obj);
} while ((m = m->d.superdata));
}
return 0;
}