Their icons in the inventory are broken, all I see is black squares faded at the edges at different rotations, with light grey half-planes (everything to one side of a straight line is light grey) sometimes. They are also called Unknown key: "<internal-name>" in the inventory.
This isn't as important as the flipping, but it would be nice to have icons if you've made them.

I'm open to PRs. The icons are just re-using one of the sprite layers. Building a better icon in the image extraction script should be doable.