[Samba] Win7 clients problem after upgrading samba file server to 4.12 on Arch

[pavlos]

Hi All,
I have a simple home network - no domain controller, no DNS, just DHCP on
my router.
I have simple samba file server built on Arch Linux, with single share
exposed and couple of client computers, some ot them running Win7 x32
(embedded, not-upgradeable), some others with different Win or Linux
systems. All of the client are connecting to the share using the same
user/pwd, set up previously on my Arch server.
The configuration was running without any issues for couple of years and
through all upgrades (rolling distro) until the last samba upgrade from
4.11.3 to 4.12.3.
Now I have problems with my Win7 clients, and only with those clients: the
message box "*The process cannot access the file because it is being used
by another process.*" popping unexpectedly in very random situations.

I have also installed new, fresh and minimal Arch Linux in Virtualbox,
added just the newest samba package, set up the simplest share with
smb.conf as follows. The same problems with Win7 clients using the new
share.

------------------------------------
[global]
 netbios name = ARCH1
 workgroup = WORKGROUP
 server string = TestSambaServer
 server role = standalone
 security = user
 guest account = nobody
 map to guest = bad user
 log file = /var/log/samba/logconf.%m
 max log size = 50

[nas]
  comment = some funny stuff
  path = /nas
  public = yes
  writable = no
  printable = no
  create mask = 0777
  directory mask = 0777
  write list = @wheel
------------------------------------

As you can see - anyone should be able to connect and read, only users
belonging to the wheel group are able to login with R/W rights.

I have also asked similar question to the marvelous Arch community, but
got nothing but a few 'mee-too' posts...

Can you, please, help me in fixing this?

   - Is it a bug symptom?
   - Or, is it a new 'feature' which i missed when reading
   release information? Maybe some defaults in smb.conf have changed and I
   should adjust them properly?
   - Or, maybe I should adjust something in Win7 configuration?
   - Or, maybe you have definitely abandoned any Win7 support and I should
   be in a deep ...trouble now?


Regards, Pawel.