Error in ClassLoader.php / File and path name length 1.2.0

[59iosl30]

Hello!

I upgraded from 0.9.4 to 1.2.0 ( on php 5.3.8 ) and everything works fine except this error in ClassLoader.php:
/srv/www/htdocs/mail/roundcubemail-1.2.0/vendor/composer/ClassLoader.php on line 393
PHP Warning:  file_exists(): File name is longer than the maximum allowed path length on this platform (4096): /srv/www/htdocs/mail/roundcubemail-1.2.0/vendor/pear/pear-core-minimal/src/MIME-Version: 1.0

The filesystem is an ext3. Any idea ?