Sometimes your database contains inconsistent data. This can happen due to erroneous client behaviour or simply by having conflicts that can happen with parallel editing on multiple devices (e.g. you delete a task on your phone while you make an edit to it on your Mac).
In such cases it can happen that your database refers to tags, projects or folders that have already been deleted.
In order to maintain consistency, FocusGTD (as well as OmniFocus) re-creates those deleted elements to the best of their abilities.