PHP5.5で、終了タグ "?>" の有無でパーサの挙動が変わるケース

a.php

<?php
declare(encoding='UTF-8');

/* あ */

b.php

<?php
declare(encoding='UTF-8');

/* あ */

?>

result

$ php -l a.php
PHP Warning:  Unexpected character in input:  ' in a.php on line 6

$ php -l b.php
No syntax errors detected in b.php

$ php -i | grep _encoding | sort -r
zend.script_encoding => EUC_JP => EUC_JP
mbstring.internal_encoding => EUC-JP => EUC-JP
iconv.output_encoding => ISO-8859-1 => ISO-8859-1
iconv.internal_encoding => ISO-8859-1 => ISO-8859-1
iconv.input_encoding => ISO-8859-1 => ISO-8859-1

$ php --version
PHP 5.5.12 (cli) (built: May  2 2014 19:53:49)
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2014 Zend Technologies
    with Zend OPcache v7.0.4-dev, Copyright (c) 1999-2014, by Zend Technologies

PHP 5.4でも再現した。

$ php -v
PHP 5.4.24 (cli) (built: Jan 19 2014 21:32:15)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2013 Zend Technologies

➜ php-5.5.14 ./sapi/cli/php -d zend.multibyte=On -d zend.script_encoding="EUC_JP" /vagrant/a.php

Warning: Unexpected character in input: ' in /vagrant/a.php on line 6
[Wed Jul 23 13:54:03 2014] Script: '/vagrant/a.php'
/home/vagrant/src/php-5.5.14/ext/mbstring/mbstring.c(612) : Freeing 0x7F34B19D51B0 (109 bytes), script=/vagrant/a.php
=== Total 1 memory leaks detected ===
➜ php-5.5.14 ./sapi/cli/php -v
PHP 5.5.14 (cli) (built: Jul 23 2014 13:46:57) (DEBUG)
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2014 Zend Technologies

php5.7.0-devでも発生

➜  php-src git:(master) ./sapi/cli/php -d zend.multibyte=On -d mbstring.internal_encoding="EUC_JP"  /vagrant/a.php

Warning: Unexpected character in input:  ' in /vagrant/a.php on line 6
➜  php-src git:(master) ./sapi/cli/php -v
PHP 5.7.0-dev (cli) (built: Jul 23 2014 15:45:55) (DEBUG)
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.7.0-dev, Copyright (c) 1998-2014 Zend Technologies

本家にissue登録した。
https://bugs.php.net/bug.php?id=67681

PHP 5.6.17でも発生。
PHP7.0.3 だと直っていた。