samba - Dec 2005 - Samba PDC keeps losing local browser status to XP boxes

I've got a random issue with a samba 3.0.10-1.4E.2 (from RHEL 4u2)
installation.

Basically everytime a pc boots up this happens:

Dec 17 06:05:43 gws nmbd[15336]: [2005/12/17 06:05:43, 0]
nmbd/nmbd_incomingdgrams.c:process_local_master_announce(311)
Dec 17 06:05:43 gws nmbd[15336]:   process_local_master_announce: Server foo
at IP 192.168.0.133 is announcing itself as a local mas
ter browser for workgroup BAR and we think we are master. Forcing election.
Dec 17 06:05:43 gws nmbd[15336]: [2005/12/17 06:05:43, 0]
nmbd/nmbd_become_lmb.c:unbecome_local_master_success(149)
Dec 17 06:05:43 gws nmbd[15336]:   *****
Dec 17 06:05:43 gws nmbd[15336]:
Dec 17 06:05:43 gws nmbd[15336]:   Samba name server GWS has stopped being a
local master browser for workgroup bar on subnet 192.168.0.10
Dec 17 06:05:43 gws nmbd[15336]:
Dec 17 06:05:43 gws nmbd[15336]:   *****
Dec 17 06:06:00 gws nmbd[15336]: [2005/12/17 06:06:00, 0]
nmbd/nmbd_become_lmb.c:become_local_master_stage2(396)
Dec 17 06:06:00 gws nmbd[15336]:   *****
Dec 17 06:06:00 gws nmbd[15336]:
Dec 17 06:06:00 gws nmbd[15336]:   Samba name server GWS is now a local
master browser for workgroup bar on subnet 192.168.0.10
Dec 17 06:06:00 gws nmbd[15336]:
Dec 17 06:06:00 gws nmbd[15336]:   *****

Now from that client's perspective, every time they try to logon to the
domain BAR they get a message saying it's unavailable until the election has
been re won by the samba server. When many machines are rebooting and coming
on line it becomes some kind of election hell. 

Here are the relevant bits on the config.

# Global parameters
[global]
        workgroup = BAR
        server string         interfaces = 192.168.0.10/24
        passdb backend = tdbsam
        log file = /var/log/samba/%m.log
        add machine script = /usr/sbin/useradd -d /dev/null -g lemon -s
/bin/false -M %u
        logon script = logon.cmd
        logon path #       logon drive = H:
        logon home         domain logons = Yes
        os level = 85
        preferred master = Yes
        domain master = Yes
        wins support = Yes
        local master = Yes

My os level used to be 33 (which is what I run on other installations fine)
but I bumped it up in a vain hope it might make it better - it didn't.

Any help gratefully appreciated!

Bruce