Is that the R3 3300?
If you watch this video at around the halfway mark Kurt takes the bag off of the frame and you'll notice that
the strap is attached to the back of the bag.
On the SG website the pictures of the backs of both the R3 5900 and the R3 7000 show that
female buckle attached to a strap feeding down in-between the frame and the bag.
I haven't had that experience. I've mostly just kept sea to summit wets wipes and an msr travel towel in there. If I ever fully unzip the bag it's on the ground so nothing falls out.