On UI2 maybe UI3 too, hidden layer always shows as having fixed state, and you can try to set it to fill or hug, but it always goes back to fixed.
This seems like a bug of implementation details leaking into the UI. Habituated users are not going to toggle layer visiblity just to change something that trivial. Then they’ll likely not notice when a change they made got silently reverted right, so time gets wasted on debugging.
It should be possible to set properties of a layer without making it visible and the UI should view the layer’s properties as they are set, not what layer hiding implementation uses.