DNS SOA problem

I have migrate from virtualmin on squeeze to virtualmin on jessie. I have the problem that SOA number is not updated when someone modify any DNS record. Could you help me ? Thanks

PS When I try to modify a record i receive this warning. On the old squeeze it doesn't matter

Warning - errors were found in this domain's DNS records : The DNS record xxxxxx.com. resolves to the IP address PUBLIC IP instead of the virtual server's IP INTERNAL IP ( i'm behind firewall in nat )