samba - Jul 2006 - Network Neighbourhood browsing, machines disappear after a while not to return until smbd restart

Hi all,  ive got an issue with not being able to see machines in network
neighbourhood after a while (ususally less than an hour).  Ive seen other posts
on these lists about this sort of issue but no answers.

When i restart samba the samba.nmbd log shows machines on my network being added
to the browse list like so.

[2006/07/12 01:00:24, 3] nmbd/nmbd_incomingdgrams.c:process_host_announce(118)
  process_host_announce: from DADSDESKTOP<00> IP 192.168.1.98 to
WORKGROUP<1d> for server DADSDESKTOP.
[2006/07/12 01:00:24, 3]
nmbd/nmbd_serverlistdb.c:create_server_on_workgroup(159)
  create_server_on_workgroup: Created server entry DADSDESKTOP of type 40011203
() on workgroup WORKGROUP.
[2006/07/12 01:00:34, 3] nmbd/nmbd_serverlistdb.c:write_browse_list(421)
  write_browse_list: Wrote browse list into file /var/cache/samba/browse.dat


After a while samba thinks the machines have expired and removes them from the
browse list at which point they disappear from the network neighbourhood only to
return if i restart samba.

[2006/07/12 01:24:42, 3] nmbd/nmbd_serverlistdb.c:expire_servers(198)
  expire_old_servers: Removing timed out server DADSDESKTOP
[2006/07/12 01:24:42, 3] nmbd/nmbd_serverlistdb.c:write_browse_list(421)
  write_browse_list: Wrote browse list into file /var/cache/samba/browse.dat

The machines are still browsable if i access them by IP or by name,  its only
the browse list they arnt showing up in.  My samba server is set to be LMB and
DMB and wins server is active,  the samba server is also my dhcp and dns server
for my lan and its running slackware 10.2.

So i guess what im asking is how to i force my windows clients to refresh with
the samba wins server box so that it doesnt think they are dead ?