That's a common issue with Trek Interchange panniers. I personally know two people who have crashed because this very same issue. I'm very surprised their engineers let a design like that through, and even more surprised their lawyers haven't made them remove them from the market. Maybe someone should phone Ralph Nader.

I've never heard of the problem with others.

Although I have had a bungee leap out of my open-top grocery pannier once, and wrap itself around the cassette. Pure rider error, that one.