[BUG] Mesh Merging results in lighting / reflection problems

[DrBlackRat]

Issue:
Now after #15 is closed I've discovered a new issue with the mesh merging.
After the meshes have been merged, I've discovered that there are now a few issues with the reflections and lighting.

Attachments:
The left side is after using Lazy Optimiser and the right is the original:

Here is the back side, the left is the original and the right is after using Lazy Optimiser:

Here are a few other screenshots: