[luatex] LuaTeX v1: Two questions from testing

[Joseph Wright]

Hello,

Testing LuaTeX v1, there are relatively few changes from v0.95. However,
I've found one logging (?) change and one hyphenation change I didn't
expect. With example

    \hsize 15em
    This is a supercalifragilisticexpialidocious%
     \hbox to 1em{}
     sentence.
    \tracingall
    \belowdisplayskip=0pt %
    $$
    y = mx + c
    $$
     \bye

The results are different from pdfTeX in two ways. The empty \hbox does
not prevent hyphenation, which it has to-date (so this is not a result
of other hyphenation changes). The log also lacks the zero skip after
the display.

It's not clear to me if either of these changes is deliberate: what's
the situation?

Josph