why diabled Phalcon\Cache\Backend\Redis the `_PHCR`prefix ?

i see the Phalcon\Cache\Backend\Redis save method code :

if keyName === null {
    let lastKey = this->_lastKey;
    let prefixedKey = substr(lastKey, 5);
} else {
    let prefixedKey = this->_prefix . keyName,
        lastKey = "_PHCR" . prefixedKey,
        this->_lastKey = lastKey;
}

it's doesn't disbaled _PHCR