Oh, that makes lots of sense! Definitely left me very confused at first, though. I wonder, should you not instantly gain that difference, rather than having it regenerate to the new maximum?

If stamina, in this context, can be thought of as a representation of your total potential max-exertion over time - inversely proportional to the total weight you're carrying - then an instant reduction in weight should result in an instant increase in your potential.

I might edit this ticket when I get a chance to better reflect what's actually happening.