You're a god dude! you saved us all fans of nep nep! , now if only someone could work their magic on world of final fantasy issues too, then i could die happy haha
There is an AMD reference ticket for this issue  OpenGL shader/texture problem for Neptunia Series games.
Also, there is a guide on steam explaining in depth how to apply the workaround similar to what whalee figured out here.
The games affected by this bug are the following:
Hyperdimension Neptunia Re;Birth 1
Hyperdimension Neptunia Re;Birth 2 Sisters Generation
Hyperdimension Neptunia Re;Birth 3 V Generation
Superdimension Neptune VS Sega
The issue is STILL present in 18.1.1
While I'm waiting for this to get fixed, I do have something good to say. I notice a framerate improvement in the new drivers despite the texture glitch. I hope they can fix this while keeping this framerate improvement.
issue fixed on version 18.2.1 no more neptune on acid, thanks to all the helpers and AMD for finally making this happen, cheers.