Hmmm... and this was a Tibuk2? I've owned two and both had the sternum straps. When I first started using it the bag would move around a lot especially when I was standing on the bike. I eventually figured out which shoulder to best wear it on (which in my opinion makes a difference) and how to properly use the sternum strap (I wasn't tightening it enough). Ever since, I've had no issues with the bag shifting. Sometimes if I have a very light load and don't secure the strap well, I'll get a little shifting.