Here's the thing. If you put stuff other than sunglasses in the sunglasses case, they may disappear.
Pens in particular can easily roll up and over the back of the case and get lost in the void behind, never to be seen again and sometimes obstructing the opening of the case.
The good news is they can be retrieved by removing the case. The bad news is that it can be a bit tricky to do without instruction. Similarly, your lenses can slide upward while carrying and obstruct the opening if gravity doesn't bring them back into place.
Going forward, we're prototyping a soft touch magnetic top/cover that would keep all items in that compartment secure from moving around. For now the right solution is still TBD.
In our earliest Packs, we had an issue where this case could pop-out during shipping. This is because it is put together using a snap-in feature which, in certain instances (like tossing around a box with some force) can pop-out the very same way it goes in.
This is why we introduced the blue "refrigerator" tape as part of our packaging. It keeps everything in its place during the tumultuous shipping stage.
We've also encountered a few occasions where a person's pack gets bumped and the same thing can happen. While it's an easy fix to re-install, we're currently exploring ways to ensure it stays in there permanently. One option is to add bolts inside to the ends of the pins on which the case pivots.