5400SM with 8.2.2: strange DHCP behaviour


all my network is composed by SM with 8.2.2 and NAT+DHCP enabled.
The Private NAT IP of the SM is So, normally, the first pc will get and so on.
NAT Public Network:
Radio Public Network:

Some of the customer (2 actually) had connectivity problems.
When I check the arp table of their SM I get the following:

Telnet+> arp -a

IP Address Physical Address iface pend c-time l-time 00-0d-b9-12-6c-19 rf2 N 44206 51950 00-05-1c-04-00-4a et1 N 3514 0 00-01-4a-c2-6b-1c et1 N 3499 26402 a0-45-be-00-01-8e et1 N 1322 1322 1a-00-3e-52-a0-45 rf1 N 1182 1193 4c-50-42-41-43-4b lo0 N 1182 1193 00-01-4a-c2-6b-1c et1 N 921 921 00-00-00-00-ff-ff et1 N 921 1619

IP Address Physical Address iface pend c-time l-time 00-05-1c-04-00-4a NAT N 3985 50394 00-0c-42-14-b4-8f NAT N 3499 4810 00-40-f4-bc-1e-61 NAT N 3478 37815

The same data are visible using web interface.
The strange thing are the two IP: and
Did anybody has the same issue?