I've just logged this with Autodesk support
Some of our isolated footings were displaying the incorrect "Bottom of Footing" elevation. I began to notice that it was only the footings which were joined to a grade beam, and then lowered. This gave me an idea: Could it be that simply Joining the grade beam to the footing was causing it to report the wrong "Bottom of Footing"?
Note: The tag uses the "Bottom of Footing" parameter, which I verified in the element properties matched the tag
Screen 1: The joined geometry with the incorrect top of footing
Screen 2: Using the Unjoin tool, simply click on the grade beam. Voila! Instant change in the parameter. (The footing did not actually move up and down)
Now you know. And knowing is half the battle.......