QTreeWidget collapseAll() collapses only visible items

I've got a QTreeWidget and want to collapse all items, so I call collapseAll(). However, this only collapses visible items, as the user can see the next time they click to expand an item: the items below, now exposed, retain their previous collapse/expand state. So I had to write a recursive-descent method that goes through the whole tree and actually collapses everything. Seems like collapseAll() ought to do this, given its name. :->