When building the Tab Panels, you do build each panel as a separate form. The one Tab Panel is simply grabbing the elements of the selected panel’s form and rebuilding them within the Tab Panel. You’re dealing with the same active record even as you change to other panels.
Even with other windows within the database open at the same time, there is only one active record at a time. But in those windows, you may very easily have different fields active while accessing that one active record. In many cases, your windows or panels may not even include the same fields.