QGraphicsItem: pure virtual method call problem

[phuongot]

Hi every body,
Please help me with this problem:
I have a class TrackObject that derived from QgsmapcanvasItem to draw a dynamic object on Map, the QgsMapcanvasItem is derived from QGraphicsItem. sometimes i get a pure virtual method call exception and the program is crashed. the "pure virtual method call" exception occured when i create a new TrackObject or delete the TrackObject. I use QGis for MAP and QT version 4.7.4 on OpenSuse OS.

the attachment is my exception.

Thanks in advance!