Your computer is turning off the USB bus when hibernating. I am not very confident in this mode, so I stay away from it: plenty of applications have issues with the refresh.
You can alter the power settings for the USB port via Control Panel > Device Manager > find the USB hub, and select the port you normally use for the Fuze. Deselect the choice “allow Windows to kill your Fuze”.
The problem with this is in Microsoft’s realm. Power management is sketchy at best in my experience. If only Microsoft had come up with some honest splash screens for us, like:
“Windows would like to go to sleep now. We’ll call it hibernate, but I think I have suffered an aneurism, and I’m going to crash. What are you doing, Dave? Daisy, daisssssssy…”
The available “percentage” displayed for the Fuze is actually the estimated amount of run time while the LiPo battery is above the minimum voltage threshold to safely deplete the cell. There is a happy margin of safety, allowing for the real world, solar wind and sun spot activity, and the time it will take a test human to get around to get around to plugging in the Fuze for some more music.
SanDisk has observed these test humans, and has video of the unhappy test subjects, heads low, some with earbuds still dangling from their newly quieted ears, looking for the nearest 30 pin USB cable. The footage of the resulting melee around the water cooler is quite graphic, and a testament to human nature. Someone made the mistake of leaving two freshly charged Sansa Clips on the tank, and a frenzy ensued.