Why does the same work item formatted ID show up in multiple workspaces with different details?
A formatted ID is only unique at the Workspace level. It is likely that a formatted ID will exist in multiple workspaces in a single subscription. This is important to know when searching for a work item by its formatted ID because when performing a search, the application takes into account the user's Workspace and Project scoping.
If the user is searching in Workspace 1 for US1234 - Fix drag and drop, but they are scoped to Workspace 2, then they will be shown results for US1234 - Fix scroll bar.