[Samba] Cannot change directory permissions

[Felix Matouschek]

Hello,
 
I occasionally need to remove the write permissions from directories inside a share to prevent users from accidentally deleting files inside that directory.
 
My problem is that I neither can view nor can change the permissions of directories on my shares.
Curiously enough viewing and changing permissions of files in the same shares works without a problem.
 
Is there anything I misconfigured?
 
My smb.conf looks like this:
 
[global]
    ### Network  ###
    netbios name = Fileserver
    server string = Fileserver (%h V:%v)
 
    ### ad member ###
    workgroup = INTRANET
    realm = INTRANET.MYCOMPANY.DE
    security = ADS
    kerberos method = secrets and keytab
 
    ### WINS ###
    wins server = 192.168.0.197
    name resolve order = wins host bcast
 
    ### logins without prepending INTRANET\ ###
    map untrusted to domain = yes
 
    ### other settings ###
    unix extensions = no
    invalid users = root
 
    ### make exe files executable on windows without x bit ###
    acl allow execute always = yes
 
    ### performance ###
    deadtime = 10
    use sendfile = yes
    socket options = TCP_NODELAY IPTOS_LOWDELAY SO_KEEPALIVE
 
    ### prevent unwanted files ###
    veto files = /$RECYCLE.BIN/desktop.ini/Thumbs.db/.DS_Store/._.DS_Store/.apdisk/._.apdisk/.TemporaryItems/._.TemporaryItems/.Trashes/._.Trashes
    delete veto files = yes
 
### SHARES ###
 
[Exchange]
    path = /home/nobackup/exchange
    guest ok = yes
    read only = no
    create mask = 660
    directory mask = 770
    force group = exchange-users
 
Greetings,
Felix