What is happening is logical and documented (see Getting Started > Tagging > Nested Tags in the built-in Help and manual).
Since those tags are contextually specific – and tags are specific to a database – do you need any kind of prefix or nested tags at all?
For example, would you be tagging something as pass for any other reason than whether a student passed or failed? And isn’t Campbell always going to be that teacher and not related to soup 
By the way, you can (and always have been able to) exclude a tag group from being used as a tag. Control-click it and choose Exclude from Tagging and it will appear as a group. But realize that tag will no longer function as a tag for any purpose in that database.