I have had MAC addresses randomly deleted in both routers. I tracked the problem to Network Magic. When I originally set up Network Magic, I gave it the router admin password. Once I changed the password, the deletions stopped.
I reported this to DLink when I bought the 4300 months ago; I was shocked to see the problem still present in the 4500.
On a related note, the 4500 has limted MAC address table editing tools compared to the 4300; I can't even input a computer name or IP address for each MAC address I've got entered.
Anyone else seen this?