samba - Mar 2013 - Winbind failing after SIGHUP

Hello,

We are using Samba (3.5.6~dfsg-3squeeze8) with Winbind to join a
Debian server to our domain for the purpose of AD authentication in
Freeradius (using NTLM_AUTH).  We actually have two of them for two
distinct domains.

One of them is behaving well.  The other one stops authenticating
every time logrotate runs on Sunday mornings.  In the logs I see:

  [2013/02/24 06:25:04.238009,  1]
winbindd/winbindd.c:256(winbindd_sig_hup_handler)
    Reloading services after SIGHUP

And I can reproduce it with:

  kill -SIGHUP `cat /var/run/samba/winbindd.pid`

Every week, at 6:25 AM on Sunday, authentication stops working, though
the daemon is still running.  What would cause Winbind to fail from a
HUP?

Thanks in advance,
Jordan