After the upgrade, the tree works as usual, preserving from one session to the other the state.
Those experiencing the problem are left in the cold. They unset the treemenu module and have to dig in the various dialog to find the offending.
In 1.16r10, the treemenu build is producing a file /var/run/treemenu.log. This file is updated after each menu entry is processed. So if Linuxconf fails in one area, you can tell where just by looking at this file.
Oddly, this treemenu build looks more and more like a crude regression testing.
The right arrow opens a closed menu, but tries to position the cursor on the line you were when you used the left arrow to close the menu.
Using both keys allows you to visit various areas in the tree menu very quickly. Give it a try.
A help screen was written and is always available while using the treemenu in text mode.