Hehe, just went out with my camera to check, mine is the same as yours, the problem I saw at the pumps last week is that the right end (looking at your photos) of the retaining strap is attached to a part that ROTATES around the screw cap, so yours is currently in 10 and 12 o'clock positions on your photos...
What I've seen happen is depending on what position that part is in can affect where the loop of that strap can go. Sometimes the loop of that strap can end up lying down the right-side of your screwcap so when the main cover tries to open, the loop of the strap gets *snagged* on the right-side of the screw cap and stops the cover opening properly if at all.
Hope that explains my understanding of it
