Yesterday I went to bed with 1100 energy, 0 to recover and 40hp/6min. It was more than 6 hours before the day change so I expected I would wake up with 1100 energy and 1100 more to recover. When I woke up after the DC, I found that I had 1100 energy but only about 500 more to recover instead of 1100.
I think the bug has something to do with the change in energy regeneration rate that drops to normal on each Tuesday. It has happened to me before at least once. Maybe if I had woken up just before the DC, the game would have registered my full 1100/+1100 and I wouldn't have lost anything but getting up before 9:00 is not my habit.