Yes, it is an eccentric bottom bracket. You can see that the actual hub is off-center (vertically in this case). The bottom bracket (the black part in the photo) can be rotated after loosening some set screws with an allen wrench in order to tension the belt. The belt doesn't stretch at all. I've been impressed by how well it maintains proper tension.

Thanks, Mike. I've always tried to shift into the lowest gear before disconnecting the cables. I think that the problems I've had have two sources. The first is that when removing the rear wheel, I've needed to remove the gizmo (I don't recall what Rohloff calls it) that attaches the cables to the hub. When re-installing it, it is not easy to align, and apparently I'm shifting up a gear when jiggling it around to get it back on. That has resulted in missing just one gear, and was the case here. The second is that there is a stiff shift between gears 7 and 8, and while it has felt as if I've shifted all the way down, I've actually only shifted half way, and haven't realized it since I'm not actually riding. I'm aware of both of these errors now, and take more care to avoid both situations. I'm aware that a lot of other Rohloff riders don't seem to have this problem, but, for whatever reason, I do. I'm glad that you're interested, and certainly welcome any tips!

I am sure you have worked it out by now but for some readers considering a Rohloff the tip is to shift into 1 or 14 before disconnecting cables because the shifter just flops around without cable tension and you may not remember what gear you were in.

Is that an eccentric bottom bracket? Does the belt stretch at all?