I'm even surprised at how many people I fly with unbuckle the shoulder straps during flight - even if allowed by the rules. I've got too many years strapped into a seat so tight that I felt like I could barely move, but I KNOW that I would forget to buckle back up again when it came time for landing.
This mishap is just hard to hear and the thought of what the victim must have felt is terrifying.

Update:
Victim's body found after search
http://www.chicagotribune.com/news/s...,3307889.story