FQDN changing to IP in XDCR cluster reference

we are using couchbase 4.0.0. we have configured the unidirectional xdcr between two clusters using fqdn.
we could see that whenever fqdn changing to ip in cluster reference dynamically when remote cluster foes down and come up.
xdcr is aware of remote cluster but fqdn which was configured is changing to node ip address whenever first node of remote cluster bring up.
is cluster not aware of fqdn or not storing any details ?please help us