The number of item that memcached-1.4.15 can keep is less than older version?

I decided to downgrade memcached because there was trouble several times in 1.4.15.
After downgrading to 1.4.14, the memcached keeps item 7% more than 1.4.15.

1.4.15 has a bug around slab allocator?
ref: https://code.google.com/p/memcached/issues/detail?id=260