Why did settings disappear / not get saved after a reboot?

Answer:

If you are accustomed to using the command line interface on routers and switches, then you are probably in the habit of saving the switch configuration before rebooting. Both the copy running-config startup-config and write memory commands can be used for this. However, the habit of automatically saving changes when using the web interface is not so well ingrained for many people. Remember to navigate to System > Save Configuration page, and click the Save Configuration button after making changes to the configuration. The Update Setting and Submit buttons on the various pages will only modify the running configuration. They will not write changes to Flash memory.