question of z-stack 2.5 multicast communication

Dear all:

The zigbee spec Revision17, page 413, line 13 says that: " Each member mode multicast message  shall be transmitted nwkMaxBrodacastRetries times".

and page 413, line 18 says that: " Unlike broadcasts, there is no passive acknowledgement for multicasts."

But because I want to check z-stack 2.5 multicast behavior, so I implement a simple application, the application flow is described as follows:

- one coordinator and two routers, after coordinator formation and two routers join to the PAN, 3 devices are all be added to the same APS group

- Coordinator multicast to this group periodically, the data cycle is 5 seconds.

- I used packet sniffer to check the multicast behavior

But my testing result is described as follows:

- When coordinator multicast, the two routers both re-multicast this packet, so this result seems violate  the spec page 413, line 13

- In other data cycle, Sometimes coordinator send this mulicast again, (so it looks like the coordinator receive no passive acknowledgement, so coordinator re-send this multicast packet), and then, of course, the both routers may re-multicast this packet, so this result seems violate the spec page 413, line18

So, can anyone share what is the z-stack 2.5 multicast behavior?Thanks a lot!

Best Regards.