Port Forward Port Ranges Would Not Work on New IP Address

From 2010-2014, our UT box has used a couple rules to port forward traffic from the outside to an internal Mitel 5000 PBX. We're in the middle of transferring to a new ISP, so the 2 external IP addresses for the Mitel VOIP server are changing.

Steps I took:

• I changed the IP in Mitel.
• I changed the IP address on the phone to match the new external address.
• I edited the existing port-forward rules in UT to use the new address.

Doh! - IP Phones could not find server.

• I spent a few consecutive weekends pulling my hair out. The problem seemed too simple to call support.
• I then fixed the problem by realizing that a single port in the range wasn't responding as it should, so I had to create a special rule for a specific port (50100), which wasn't previously required. Note, the preexisting rule references ports 50098-50508. Port 50100 should have been honored inside that range.

Why would a range of ports work for my old address, however not work for my new IP address? Thinking I was going nuts, I changed everything back to the old address and disabled the new port-forward rule. Reverting it back to the old address with a port range worked just fine, like it had for years.

If anyone has a clue, I'd love to solve this mystery. I wouldn't want to have to open a rule for every single port that the Mitel wants open. Fortunately, just adding a single rule for 50100 was all it took. I also feel there have been other examples where port ranges would not work effectively.

Also, are there online guides for the syntax in specifying noncontiguous port ranges (e.g 15,200-206,30088).

Cheers,
Ron