samba and file locks

[FreeBSD]

Hello,

I have a problem with file locks on share. My server is running
FreeBSD 10.2 (amd64), samba 4.3.3 (ROLE_ACTIVE_DIRECTORY_DC) and ZFS
pool (raidz) as a windows share.
There is a strange behavior when I open a file from one windows
workstation (smbstatus shows DENY_WRITE and everything seems right) and
after about 5 minutes later I open the same file, which is still edited
on first computer, from other windows workstation. At this moment I
should see a warning message which inform that the file is going to be
opened in read-only mode but nothing happen. The file is opened normally
in read-write mode, so I can write into this file from both workstations
at the same time overwriting data! It looks like the file lock doesn't
work any more.

log.smbd shows:
../source3/smbd/close.c:268(close_remove_share_mode)
close_remove_share_mode: Could not get share mode lock for file
data/filename

I noticed the same situation with share based on UFS.

Below is my smb4.conf.

[global]
        dos charset = CP852
        unix charset = ISO8859-2
        workgroup = WORKGROUP
        realm = somedomain.int
        server role = active directory domain controller
        passdb backend = samba_dsdb
        min receivefile size = 16384
        kernel change notify = No
        dns forwarder = 192.168.1.1
        nsupdate command = /usr/local/bin/samba-nsupdate -g
        rpc_server:tcpip = no
        rpc_daemon:spoolssd = embedded
        rpc_server:spoolss = embedded
        rpc_server:winreg = embedded
        rpc_server:ntsvcs = embedded
        rpc_server:eventlog = embedded
        rpc_server:srvsvc = embedded
        rpc_server:svcctl = embedded
        rpc_server:default = external
        winbindd:use external pipes = true
        idmap config nc:range = 10000-20000
        idmap config nc:backend = ad
        idmap_ldb:use rfc2307 = yes
        idmap config * : backend = tdb
        aio read size = 16384
        aio write size = 16384
        aio write behind = true
        write cache size = 262144
        map archive = No
        map readonly = no
        store dos attributes = Yes
        vfs objects = dfs_samba4 acl_xattr

[sysvol]
        path = /var/db/samba4/sysvol
        read only = No
        vfs objects = acl_xattr

[SHARE1]
        comment = SHARE1
        path = /mnt/zfs_share/SHARE1
        read only = No
        guest ok = Yes
        map acl inherit = Yes
        oplocks = No
        level2 oplocks = No
        vfs objects = zfsacl
        nfs4:chown = Yes
        nfs4:acedup = dontcare
        nfs4:mode = simple

Is this a bug in samba? Or I missed something.

Thank you for any suggestions.

Regards

Lukasz