Question, when you zip your backpack, do you have both zippers in the middle at the top, or off to the side? I'm asking because I had a friend lose a bunch of shit because he made the critical mistake of having his zippers at the top. Wind gets in there and away it goes!
Evilaugust you are dead on! It took me a little while to think it through, but I came to the same conclusion. The backpack was full to the brim with the liner at the top and the zippers meeting at the top. On my ZRX1200R and my YZF600R I've never ridden for an extended period of time with the backpack full and from what I recall I usually keep the zippers closed to one side or the other. In fact, when the police gave me my stuff in the "evidence" bags at the hospital, the zippers of the backpack were opened enough for the liner to come out and were at the top.
From now on I'm going to go a step further from always making sure the zippers are closed to the side, I'm going to secure them every time with something like a mini carabiner.