Try the following at a shell prompt:

% cat <<EOF | php
=====
<?php
//echo '?>';
?>
=====
EOF

The output will be:

=====
';
?>
=====

It looks like the parser is picking up the adjacent '?' and '>' characters inside the single quotes in the echo statement after they've been commented out using '//'.

I'm willing to bet 10-to-1 this is not the correct or desired behavior.