On fetching a WSDL from a OSB Cluster (ManagedServer1 ... ManagedServerN) with a load balancer sitting in front and if the endpoint URL gets set to a particular ManagedServer (Host/Port), then you cluster is not load balanced. If the client application caches the WSDL then you are in deep trouble and is not the right behaviour. In order to make it correct, do the following:
Put the LoadBalance (IP/Port) in Weblogic Admin Console at the following location:
Home -> osb_cluster ->Summary of Environment ->Summary of Clusters -> osb_cluster -> configuration -> HTTP sub-tab
Restart the managed servers and try fetching the WSDL and the endpoint service URL should be set to LoadBalancer (IP/Port) and not any of Managed Server (IP/Port). This should be done for every OSB Cluster with a load-balancer in front