ok, now I know why the destructor was commented out in prop_picker.cxx:

ok, now I know why the destructor was commented out in prop_picker.cxx:
there's a bug that I had copied: update() checks each list node: if it
has no children, then a listener is attached. Later, when freeing the
children list, it assumed again that each node without children would
have a listener attached. This caused a crash when a node had children
before, but lost them in the meantime. Now we tried to remove a listener
where there never was one.