The previous comment is from April 2013, it has a link pointing on current master, so things are changed since 2013 in the source code.
Maybe the right link is
https://github.com/php-memcached-dev/php-memcached/blob/80cb21467a1db6b7b18725df586f11801c823695/php_memcached.c#L1219
By the way, can someone skilled in C confirm the "fake setMulti" problem?