Tree tooltip 'sticks'

I have a QTree with a backing model.  When data() is called for role Qt::ToolTipRole - on cells that I've setup to have a tooltip - the tooltip displays.  But it does not go away on its own.  Even when I hover over another cell with a defined tooltip, the method is called to display the new tooltip, but, the old tooltip remains, at the old location.

I can click on another row without a tooltip to cause the existing tooltip to disappear.  When I then hover over another cell, the same thing occurs.