Bfres vertex attribute edits don't save (Wii U)

So I want to add tangents (and bitangents) to a custom model (for botw).
- I load the bfres into smash forge
- Select the model (link) in the model list
- Right-click and choose: "Generate Tan/Bitan"
- Check in Viewport > looks right
- Select bfres in model list
- Right-click and choose: "Save"
- Save file as new *.bfres

To validate the saved file I load it right back into smash forge but the tangents / bitangents are again missing.
To be sure I checked every time via "Polygone Editor" the content of the _t0 buffer for example. After reloading all values are back to zero

Then I do a file compare with winmerge: Both the original file and the saved file are identical.

Start by reproducing the reported Smash Forge workflow: generate tangents and bitangents for a model, save the BFRES, reload it, and inspect the _t0 buffer in Polygon Editor. Compare the original and saved files; the issue is done when the generated attributes persist after reload and the saved file reflects the edits.

Written by the indexing model from the issue text.