QFile opened in QIODevice::Append mode working unexpectedly`; is it a Qt bug?

In my class StudentTable I create a function appendRecord as follow-

 qint64 StudentTable::appendRecord(Student student){
QFile file(tableName);
QDataStream stream(&file);
qDebug()<<file.open(QIODevice::Append);
qint64 dumpPosition=file.pos();
qDebug()<<file.openMode();

qDebug()<<dumpPosition;
student.next=-1;
student.print();
stream<<student;
file.close();
return dumpPosition;}

The problem is that when I call the function from main() function directly it works fine. But when I call the same function from the other function in the same class it does nothing; means does not append anything to the file;

Also tried QIODevice::Append, QIODevice::Append|QIODevice::ReadWrite but nothing works for me. I tried because this question : Open QFile for appending says to try something another way; comment of the accepted answer.

I am trying to make a file for students which keeps record of the students. making a record based flat file database; using linked list.

Code: AddRecord() is calling the function appendRecord() in this case nothing happens. But when calling from main() function it appends records in the end.

StudentTable.cpp

#include "studenttable.h"
#include<QtGui>

#include "header.h"

StudentTable::StudentTable()
{
    tableName="Student";
}

void StudentTable::create()
{
    QFile file(tableName);
    if(file.exists())
        return;
    else
        file.open(QIODevice::Append);
    QDataStream stream(&file);

    Header header;
    header.magicNumber=2015;
    header.streamVersion=stream.version();
    header.used=-1;
    header.free=-1;
    header.usedLast=-1;
    header.freeLast=-1;

    stream<<header;
    file.close();

}

void StudentTable::setHeader(Header header)
{
    QFile file(tableName);
    if(!file.exists())
    {
        qDebug()<<"File "<<tableName<<" doesn't exists";
        return;
    }
    file.open(QIODevice::WriteOnly);
    QDataStream stream(&file);

    stream<<header;

    file.close();
}

Header StudentTable::header()
{
    QFile file(tableName);


    file.open(QIODevice::ReadOnly);
    QDataStream stream(&file);
    Header header;
    stream>>header;

    file.close();
    return header;
}

bool StudentTable::isEmpty()
{
    Header head=header();
    if(head.used==-1)
        return true;
    else return false;
}

bool StudentTable::isHeapAvailable()
{
    Header head=header();
    if(head.free==-1)
        return false;
    else return true;
}

 qint64 StudentTable::appendRecord(Student student)
{
    QFile file(tableName);
    QDataStream stream(&file);
    qDebug()<<file.open(QIODevice::Append);
    qint64 dumpPosition=file.pos();
    qDebug()<<file.openMode();

    qDebug()<<dumpPosition;
    student.next=-1;
    student.print();
    stream<<student;
    file.close();
    return dumpPosition;
}

 void StudentTable::print()
 {
     if(isEmpty())
         qDebug()<<" Table is empty";
     else
     {
         Header head=header();
     QFile file(tableName);
     file.open(QIODevice::ReadOnly);
     QDataStream stream(&file);
     file.seek(head.used);

     Student current;
     stream>>current;
     current.print();
     while(current.next!=-1)
     {
         file.seek(current.next);
         stream>>current;
         current.print();

     }
     file.close();
     }

 }
bool StudentTable::addRecord(Student student)
{
    if(isEmpty()&&!isHeapAvailable())
    {
        qDebug()<<"case 1";
        student=Student("rajesh","ramesh",4,5,6);
        qint64 dumpPosition= appendRecord(student);
        Header head=header();
        head.used=dumpPosition;
        head.usedLast=dumpPosition;
        setHeader(head);
        return true;
    }

    if(!isEmpty()&&!isHeapAvailable())
    {
         qDebug()<<"case 2";
         qint64 dumpPosition= appendRecord(student);
         Header head=header();

         head.usedLast=dumpPosition;
         setHeader(head);
         return true;
    }

    return false;

}

QStandardItemModel * StudentTable::getModel()
{
    QStandardItemModel *model;
    return model;

}

main.cpp

#include "widget.h"
#include <QApplication>
#include "Student.h"
#include "studenttable.h"
#include<QDebug>
#include<QtGui>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    StudentTable studentTable;
    studentTable.create();
    Header header;
    header=studentTable.header();
    header.debug();

    for(int i=1;i<2;i++)
    {
        Student student = Student("ram","bhairu",i,i,i);
        studentTable.addRecord(student);

    }

header=studentTable.header();
header.debug();

//studentTable.print();

    Widget widget;
   // widget.table->setModel(model);
    widget.show();

    return a.exec();
}