Just found couple of strange things which might be possible bugs. Tried on 310, 560,U,D, 565, 580 firmware 4.0.6
1. I've set PPTP server encryption level to Strong, but once I reboot the unit it changes to Some
2. When adding or deleting Aliases to interface (network setup) once you press finish botton or delete icon gui changes to the network setup. I rekon it should stay on aliases page.