Treeview item indicators in image-based themes vs Tk 9

Hello all,

I've recently switched to tcl/tk 9.0 and I discovered what seems to be an
issue with image-based themes having an image for the treeview item open/
close indicators.

In tcl/tk 8.6, the styling for these indicators are usually done via
something like this:

ttk::style element create Treeitem.indicator \
              image [list $image_for_closed \
                  user1 $image_for_open \
                  user2 $image_for_no_children \
              ] ...

But this doesn't seem to work in tk 9: now all items have an indicator
showing the image_for_closed whether they have children or not, and
whether the item is opened or not.

I suspect a change in the names for the states "user1" and "user2" - which
were admittedly not very user-friendly - but I just can't find any
reference for these, and by what I should replace them in tk 9 if that's
indeed the problem.

Any pointers would be greatly appreciated.

Thanks!
--
 Eric