[texhax] \mark causing a blank line

[bnb at ams.org]

    The plain TeX code below might not be a minimal example, but it's
    self-documenting!

    Stan

    %%%%%%%%%%%%

    This sentence's length and the use of a mark create an unexpected blank line
    below for some reason..... \mark{mark}

    Removing one period after ``reason'', or the space before the mark, makes
    the blank line disappear. (I'm not saying that putting a space there makes
    sense.) Does anyone know why this happens? My only guess is that the mark
    prevents the space before it from being removed when TeX breaks the text
    into lines. I'm not sure if this is a bug, but it seems odd, at least.

    \bye

your conjecture is correct -- the \mark
*does* inhibit removal of the space, and
that is forced to the next line, which
remains empty in the output.  you should
also get an "underfull hbox 10000" in
the log.

not a bug.  just one of the idiosyncracies
of the tex design,
                                                -- bb