I mentioned back in 2018 some issues regarding vertex normals being distorted when corrective shapes are enabled, and also the exporter's complete failure to properly calculate shape key normals from an object that is exported with custom normals enabled. I am just making this post to bring attention to this fact as it still has not been fixed in even the most recent release, and makes working with custom normals and corrective shapes a huge pain, basically requiring a total switch to 3DS Max or Maya for proper export.

1. A mesh with custom normals enabled and shape keys will not interpolate the vertex normals for it's shape keys correctly in Source unless a Data Transfer modifier using the "Topology" setting is enabled, transferring normals from a duplicate object in the scene. Failure to set this before export will result in shading errors from incorrect normals. This issue was not present in SMD/VTA exports prior to 2.7

2. Corrective shape keys that trigger from 3 or more shapes (A_B_C) distort the vertex normals, even if no actual vertices end up changing their position in 3D space. This issue also appears on ANY kind of corrective shape if the base object has custom normals set during export. I recorded a video demonstrating this problem during a discussion with Game Zombie, author of the 3DS Max Source Plugins, which is currently the only way as far as I'm aware to get a proper export for these cases.

https://www.youtube.com/watch?v=PLwBWWwurhI

I would really like to see these issues fixed, as someone who works excessively with custom normals and more advanced shape key structures, it has been a major hindrance on my workflow.

As always, thank you for the consideration. I can provide more information if necessary.