[PyQt] How to close QSqlDatabase connection?

[Sibylle Koczian]

Hello,

I'm trying to write a very small database application, but I can't get rid of 
this error message when I close the main 
window: "QSqlDatabasePrivate::removeDatabase: 
connection 'qt_sql_default_connection' is still in use, all queries will 
cease to work."

At the moment I'm using this code to open and to close the database:

Global function of the module:
def visa_conn():
    db = QtSql.QSqlDatabase.addDatabase("QSQLITE")
    db.setDatabaseName("/home/sib/pfotweg/visa_s.db")
    return db.open()

Method of the main window, connected with a button:
    def close(self):
        db = QtSql.QSqlDatabase.database()
        db.close()
        db.removeDatabase(db.connectionNames()[0])
        QtGui.QMainWindow.close(self)

And the main() function:
def main(args):
    app = QtGui.QApplication(args)
    if not visa_conn():
        QtGui.QMessageBox.critical(None,  ...)
        sys.exit(1)
    visa_mf = VisaMF()
    visa_mf.show()
    sys.exit(app.exec_())

I found some posts to this list in the archive with the same error, but no 
solution. I've tried to use 'qt_sql_default_connection' as argument to 
db.removeDatabase, but that doesn't change anything. What's wrong? Or what 
additional info should I give?

Using qt-4.3.1, PyQt4-4.3.1, Python 2.5.1, Gentoo Linux.

Thanks for every hint,
Sibylle

-- 
Dr. Sibylle Koczian