Author list goes outside margins in the ACM SIGCHI template

Question

For some reason having 4 authors in this ACM SIGCHI template renders it outside the right margin. See more details and image here.

I suspect the problem is with .cls but I have no idea where to start. Here are the relevant lines in the .tex source:

\numberofauthors{4}
\author{
  \alignauthor Aaaaa Aaaaaaa\\
    \affaddr{Affiliation}\\
    \affaddr{Affiliation}\\
    \email{author@a.com}
  \alignauthor Bbbbbbb Bbbbbb\\
    \affaddr{Affiliation}\\
    \affaddr{Affiliation}\\
    \email{author@b.com}
  \alignauthor Cccccc Cccccc\\
    \affaddr{Affiliation}\\
    \affaddr{Affiliation}\\
    \email{author@c.com}
  \alignauthor Ddddddd Dddddddd\\
    \affaddr{Affiliation}\\
    \affaddr{Affiliation}\\
    \email{author@d.com}
}

\maketitle

Answer 1

If the template is the same as what you can get from http://www.acm.org/sigs/publications/proceedings-templates then have a look at question 18 in their FAQ (scroll, don't click).

Answer 2

The class seems explicitly set up for maximum 3 authors. For more than 3 it seems to want you to do something like:

\numberofauthors{5}
\author{
  \alignauthor Author 1\\
    \affaddr{Affiliation}\\
    \affaddr{Affiliation}\\
    \email{author@a.com}
  \alignauthor Author 2\\
    \affaddr{Affiliation}\\
    \affaddr{Affiliation}\\
    \email{author2@b.com}
  \alignauthor Author 3\\
    \affaddr{Affiliation}\\
    \affaddr{Affiliation}\\
    \email{author2@b.com}}
\additionalauthors{Author 4, Author 5}

Which puts an "additional authors" section at the end, before the references...