I'm seeing this same issue on CentOS 5.6 and Ubuntu 12.04.
CentOS 5.6 with libmemcached version 1.0.4-3.el5
Ubuntu 12.04 with libmemcached version 0.42 and 0.44
As libmemcached evaluates the expire time differently depending upon if the seconds passed are < 30 days, it's worthwhile to note the same anomaly is seen with a much smaller value.
I'm seeing this same issue on CentOS 5.6 and Ubuntu 12.04.
CentOS 5.6 with libmemcached version 1.0.4-3.el5
Ubuntu 12.04 with libmemcached version 0.42 and 0.44
As libmemcached evaluates the expire time differently depending upon if the seconds passed are < 30 days, it's worthwhile to note the same anomaly is seen with a much smaller value.
echo "Y" > testkey
memcp --verbose --debug --servers=localhost --expire=120 testkey
op: set
source file: testkey
length: 1
key: testkey
flags: 0
expires: 288