Child QGraphicsItem setToolTip does not override parent QGraphicsItem's tooltip

[philw]

My QGraphicsItem subclass "parent" item contains two nested levels of children QGraphicsItem [in Qt 4.6.3]. I want the lowest level child QGraphicsItem (a QGraphicsRectItem) to have a tooltip which OVERRIDES the parent's tooltip. But only the parent tooltip is showing up.

The child QGraphicsItem is calling this method in its constructor:
setAcceptHoverEvents (true);

The containing QMainWindow subclass constructor -- and also the QGraphicsView subclass constructor -- are calling this:
setAttribute (Qt::WA_AlwaysShowToolTips);

Why isn't the nested child QGraphicsItem's "setToolTip()" having an effect?

Thank you in advance,
Phil Weinstein, CADSWES
Boulder CO USA