[Samba] Samba 4 - problems with name resolution on Windows 7 clients

[X-Dimension]

We have a strange name resolution problem on Windows 7 clients. (Windows 
XP clients are working fine!)
If a Windows 7 client is connected more than 7 or 8 hours to our Samba 4 
active directory server, we can't
do "ping servername" anymore, but "ping servername.domainname" works fine.
After logout and login again to the Windows 7 clients everything works!
The main problem is, that all Windows clients access the samba shares by 
\\servername\sharename
and not \\servername.domainname\sharename and after 7 or 8 hours our 
users can't access the files
or programs on these shares.
What goes wrong here and what is the best way to fix this? I can change 
some GPOs and set all
shares to \\servername.domainname\sharename, but if there is a better 
solution i would prefer this.
Thx for help! :)