Unexpected CAS behavior

Setting values through CAS with a cas_unique of 0 has an unexpected behavior.
It seems possible to set through CAS a non-existing key if you use a cas_unique of 0. This seems different from the implementation of memcached that I compared it against, which wouldn't let you store through CAS if the key didn't exist. Using it this way it is effectively working as an ADD.

This is not a big deal as it is, the real problem is that you can also set it through CAS with a cas_unique of 0 if the key already EXISTS and it has a cas_unique different from 0. I'd expect this to fail, since the cas_unique doesn't match the one in the existing key.

See example, for membase 1.7.1, connected through telnet to port 11211.

flush_all
OK

cas test 0 0 1 0
a
STORED

gets test
VALUE test 0 1 67969
a
END

cas test 0 0 1 0
b
STORED

gets test
VALUE test 0 1 67970
b
END