"Overfull \hbox (4.592pt too wide)" on the \end{document} line, triggered by sigconf title/author display

[zackw]

A document satisfying all of the following conditions...

1. Class option sigconf is in use
2. There are at least two authors
3. Both of them have complete \affiliation blocks
4. There is an \authornote

... will throw an "overfull \hbox" warning --- with the line numbers pointing not to the \maketitle, as one might expect, but to the \end{document} line, even if that's thousands of words and multiple \clearpages later. Moreover, no matter what the \overfullrule is set to, there will be no indication in the PDF of where the problem is.

This should be a sufficient and close-enough-to-minimal test case:

\documentclass[draft,sigconf]{acmart}
\begin{document}
\title{Overfull \textbackslash{}hbox at end of document}
\author{Alice Able}
\affiliation{
    \institution{Institute for Debugging}
    \city{Null Island}
    \country{Ghana}
}
\authornote{This seems to be necessary}
\author{Bob Baker}
\affiliation{
    \institution{Institute for Debugging}
    \city{Null Island}
    \country{Ghana}
}
\maketitle
\end{document}