[luatex] Hyphen char vs discretionary (bug?)

[Javier Bezos]

With the following document:

-------------------------
\directlua{

function test (head)
   texio.write_nl('====')
   texio.write_nl('')
   for item in node.traverse(head) do
     if item.id == node.id'glyph' then
       texio.write(unicode.utf8.char(item.char))
     else
       texio.write('[' .. item.id  .. ']')
     end
   end
   return head
end

callback.register("pre_linebreak_filter", test)
}

12-34

\bye
-------------------------

TexLive 2017 (1.0.4) showed:

[9][0]12-34[14]

But with 2018 (1.07) I get:

[9][0]12[7]34[14][12]

In other words, the hyphen char has been replaced
by a dicretrionary.

Cheers
Javier