After some more works, the problem could be change.
In fact, during the treatement I apply on each items, I use the method :
@void QTreeWidget::setCurrentItem ( QTreeWidgetItem * item, int column, QItemSelectionModel::SelectionFlags command ) @
to change their selection.
It turns out that the fact of using such a method on items that are too deep into the tree for being directly visible automaticaly makes the view of the tree change in order to make them visible.
Of course I don't want the view of the tree to change when those action are performed.
Anyone has a idea to forbid that update of the display of the tree?
thanks