samba - Jul 2006 - Unable to modify SID for "administrator"

Whenever I try to change the samba password for administrator, I get the 
following error:

---
Unable to modify TDB passwd ! Error: Record does not exist
 occured while storing the RID index (RID_000001f4)
Failed to modify entry for user administrator.
Failed to modify password entry for user administrator
---

I deleted the administrator account from the database (I'm using tdbsam), 
and despite seeing the message "Unable to delete user administrator",
it had
actually been deleted (I checked with pdbedit -L)

I then added the administrator account using 'smbpasswd -a
administrator'

I then try to change the SID of this account to -500, using pdbedit, and I 
get a similar error to the above:

---
Unable to modify TDB passwd ! Error: Record does not exist
 occured while storing the RID index (RID_000001f4)
Unable to modify entry!
---

All other accounts are absolutely fine.  Is there something special about 
administrator?

Many thanks,
Steve :)

After changing the SID of any account, eg:

pdbedit -U S-1-5-21-2411803954-1159576741-3064619986-500 -u administrator -r

...the SID *is* changed successfully, but I get the following error:

---
Unable to modify TDB passwd ! Error: Record does not exist
 occured while storing the RID index (RID_000001f4)
Unable to modify entry!
---
>From this point on I am no longer able to change the password using 
smbpasswd.

Using pdbedit -x to remove the account gives the error "Unable to delete 
user <user>", but pdbedit -L doesn't list the account any more.

Using tdbdump I find there is a remnant left over in passdb.tdb.  Eg:

{
key(13) = "RID_00000bbc\00"
data(5) = "test\00"
}
{
key(13) = "INFO/version\00"
data(4) = "\02\00\00\00"
}

This problem only happens after changing the SID on an account.  Is it a 
bug?

Many thanks,
Steve :)

Is this a bug?