Private VLAN Edge / Protected Port

Hello!

I have question regarding Protected Ports on Dell Powerconnect 6248.

What I want to achieve - two devices one connected to port39 and other to 40 can not talk to each other. I assumed that this can be done straight forward with "Protected Ports" feature.

So I created:
switchport protected 0 name "A"
switchport protected 1 name "B"

interface ethernet 1/g39
switchport access vlan 3
switchport protected 0
exit
!
interface ethernet 1/g40
switchport access vlan 3
switchport protected 1
exit

Some testing - connected one device with IP 192.168.7.10 (random IP from local IP address range) to port39 and another device with IP 192.168.7.11 to port40. When I perform PINGs these devices can ping each other.
What is wrong with my configuration or "Protected Ports" works in different way?
And why there is groups (in example I created A and B) - in manual I cant find any explanation on them.