[Samba] uaser added to a local group doesn't get permissions

[Gianluca Cecchi]

I have a share like this

[share_name]
   comment = share name
   path = /home/col/services
   browseable = no
   valid users = +servizi
   force group = servizi
   public = no
   writable = yes
   create mask = 0770
   directory mask = 0770
   printable = no

In 2.2.5 as I added a user to the "servizi" group in /etc/group, the
user was able to connect directly from his/her already open session
and eventually map the share as a network drive.
Instead in samba samba-3.0.9-1.3E.10 (RH EL 3.7) this seems not true.
The user has to disconnect from his/her windows session and then
reconnect to get access to the share, otherwise he/she gets prompted
for a user/password prompt   (and using the right values doesn't work)
Searching through samba bugzilla I didn't find same error.
Actually something similar: bug 3423 where it seems that this is a
feature (behaviour such as windows) and not a bug. is this the case?
So it was a bug in 2.2.5....?

Thanks in advance.
Gianluca