[Samba] Archive attibute bit management question

[Thierry Terrier]

Hi,
I'm trying to use the archive attribute for backup purpose. All is ok 
with own user management but not for the group.
The accounts user1 and backup are in the staffgroup. *The backup account 
is not in the admin. group*.
It seems that the archive bit can't be changed with file write access 
granted. This bit is mapped to the UNIX owner execute bit.
The create mask parameter is set such that owner execute bit is not 
masked out.

Here is my share configuration:
map archive = yes    (default)
[User1]
  path = /var/staff/user1
  comment = User1 archives
  public = no
  printable = no
  writable = no
  read list = backup @staffgroup
  write list = backup user1
  create mask = 0740
  directory mask = 750

I tried to set    rw?rwx---    file.tst    user1 staffgroup
for group writable permission but the '?' owner execute bit can't be 
changed.
the Debug trace show:
smbd/dosmode.c:unix_mode(111) unix_mode(file.tst) returning 0740
smbd/dosmode.c:unix_mode(111) unix_mode(file.tst) returning 0640
smbd/error.c:error_packet(91) error string = Permission denied

It seems that only the user or the super user can be change the owner 
execute bit (coming from OS).
I have tested it with 2.2.3a & 2.2.8a version.

My question is:
Is the smbd process use root rights to set/clear this bit ?

Best regards