Couchbase PHP SDK increment - expiry doesn't renew

I’ve discovered that when using the couchbase php sdk, while calling increment() with a flag to create if not exist works just fine and the expiry is respected in this case – if I subsequently call increment() in this key which now exists, the expiry doesn’t get renewed with the parameter I pass in this last time.

I suspect this is because couchbase natively doesn’t support create-if-not-exist for increment commands and simply does a set/add on client code. Therefore if the normal increment is successful (key exists), the expiry parameter is simply ignored. Is this assumption correct?