In version 1.3.6 here was a bug introduced when using Store method:
I upgraded to version 1.3.7 and it looks like this issue is still happening.
When I pass TimeStamp to Store method they don’t expire at all.
Would you mind creating an NCBC (http://www.couchbase.com/issues/browse/NCBC) and attaching an example project? In the meantime, you can try the workaround described in the link you provided:
TimeSpan validFor = new TimeSpan(0, 0, 59); DateTime expiresAt = DateTime.UtcNow.Add(validFor); client.ExecuteStore(StoreMode.Set, "test1234", "blabababla", expiresAt);