class QSqlTableModel doesn't free resources

The deleting of object of class QSqlTableModel doesn't work well. I wanted to code MDI application for working with databases and used QSqlTableModel class for convinient information exchange with databases. I allocated the object of class QSqlTableModel in heap, it's parent was dialog window with the attribute Delete_on_close. After deleting dialog window QSqlTableModel object didn't free associated database, the file was busy. I sure that it's problem of the class.