I have the same issue per computer. For each local admin account and each machine, I have an entry.
Computer1 hardware
Computer1 backupadmin
Computer2 hardware
Computer2 backupadmin
Computer3 hardware
Computer3 backupadmin
Both user accounts are local admins on a multitude of pc's and those are all showing up as well.
I can only get them to be removed from the unauthorized administrators list by adding each machine and the respective account individually. I have tried to change the table to allow nulls in the domain field and it still doesn't remove them. In version 3.5 this works as described.
I can provide a screenshot if needed to assist.