tdf#114788 help needed on SvTreeListBox usage

Hi,

So, Base has (file svx/source/form/filtnav.cxx) class
FmFilterNavigator which is a SvTreeListBox. (See
https://bugs.documentfoundation.org/114788 for how to display it.)

The structure on screen looks like (for example):

MainForm
 Or
  ID: 5
 Or
  f1: 'blah'


The issue is:

 "MainForm" should _not_ be editable. If the user clicks on that, it
 should maybe expand/collapse children, BUT DON'T ALLOW THE USER TO
 EDIT the "MainForm" string.

 "Or" should likewise _not_ be editable.

 The children of "Or" should _be_ editable.

The situation now is that this is inverted. What should be editable is
not, and what should not be is. This has been traced back to
"somewhere between LibreOffice 5.0 and 5.1", but I cannot for the life
of me find the bit of code that decides what is editable and what is
not.

I looked at
 git log -p libreoffice-5-0..libreoffice-5-1 -- svx/source/form/filtnav.*

but that didn't bring any inspiration of why this regression was
introduced in 5.1.

Some kind soul that knows about SvListTreeBox could help us there?

Thanks in advance.

Lionel