samba - Dec 2010 - shares are mounted but not always shown in "My Computer"

Hi,

 in a new installation of a pdc (ubuntu 10.04+samba 3.4.7)  I
configured a netlogon script to automount shares on clients[1] but
something of strange happens: shares are mounted but not always shown
in "My Computer" :-/ ...

My script simple execute "net use" :

  net use X: \\my-pdc\my_smb_share /persistent:no

The command always returns no error and if I execute "net use" in a
new dos-prompt I can see all my shares correctly mounted BUT if I open
"My Computer", it doesn't show me any sambashare :/. The shares
are
mounted but not shown in "My Computer".

I tried then to login a second time with the same user, the logon
script started and magically I found my shares correctly shown in "My
Computer".

Any idea on what could cause the problem or suggestion about how to investigate?

Thanks in advance!,
 Simone

[1] Windows Xp 2002 Sp3 (previously joined in a win2k3 server domain)