Lufe and I guess that we have a problem with the Windows NFS client. The client is only NFS 3 and the Server is NFS 4. According to the URL below it should work with NFS 4 but we didn't test it (yet).
The NFSv4 client is required to renew its leased in a fixed, known time before the term of the lease expires. If the client fails to renew in time the locks it has are subjection to revocation. So lets say the client crashes and never restarts. Then the locks it had will automatically expire, allowing other clients to acquire the locks.
When an NFSv4 server restarts, as with NLM, there is a grace period for reclaim. But there is no NSM-like notifications to the client nor are any needed. Because the client has to renew its lease, it will eventually find out about the server restart on a renew attempt. The grace period is at least as long as the period of the lease, allowing any client that had locks sufficient time to find out that it has lost its lease and its locks. Thus it is not possible for to clients to think they have the same lock on the same file.