It's been broken for a long time. If you use all your stamina and turn off the game, the timer gets reset if you log in during a period of time between the 2 hour marks.
Whether it's been 3 hours or 2.5 hours, if you log back in the timer will show 1h59m and you have just 1 stamina point. Obviously the timer sets back to the 2 hr window upon your login, not the 1.5 or 1 hour you would expect based on true time elapsed.