It's because you haven't thought out multiple php configuration. Each version must have its own modules!
Othewise php for 'multiple php' running well. Default php (install with 'yum install' or 'yum replace') have a trouble with php53s.
You can test php for 'multiple php' with:
1. run 'sh /script/php55m-installer' --> truly it's will be process the php55u from IUS
2. run 'service php-fpm stop'
3. run 'mv -rf /etc/rc.d/init.d/php-fpm /etc/rc.d/init.d/php-fpm.old' and then 'cp -f /opt/php55m/custom/php-fpm.init /etc/rc.d/init.d/php-fpm; chmod 0755 /etc/rc.d/init.d/php-fpm'
4. run 'service php-fpm start'