Apparently I've got some kind of nasty in my PC. My Advanced IP Scanner started doing strange things, like repeating the same device under different IP Addresses (duplicating MAC Addresses and all!) It doesn't save my renaming, and it copies comments to other devices. I thought I had a bad install, so I uninstalled and downloaded the latest version. That didn't cure it, so I'm going to try a reboot, and if that doesn't work, I'm going to tear apart my laptop to figure out what the hell is going on.
Before I do that, though, has anyone else seen this problem?
You need to delete stored data. You can find this option in the following way: Advanced IP Scanner -> Settings -> Options -> Misc -> Delete stored data.