No, it's not normal, and should't happen, but it won't cause any problems, other than having multiple UNINS000.EXE files in your FSX root folder (but don't touch them) taking some space for nothing, and those entries use each one a registry entry. Not that this makes any difference, since it's very likely you have thousands of unused registry entries coming from every kind of software.
But these are all cosmetic issues, there's only one Addon Manager installed at any time, the Control Panel list it's just a list of available UNINSTALLERS so, what you are really looking at, is that you have a single program that can be uninstalled with many different uninstallers.
If you run through them all, it will uninstall the Addon Manager the first time you click on an entry, and will remove the multiple entries when you click on the other ones so, if you want to remove them all for your own peace of mind (and reinstall it just once at the very end), your Control Panel will look cleaner, but of course it won't make the slightest difference to the installed program.
