USD referenced as stage has wrong material

**Describe the bug**
When I export my model from 3ds Max with material to usd and then I import it back. With direct import it looks alright but referenced as stage has wrong material.

**Steps to reproduce**
Steps to reproduce the behavior:
1. Create material and assign it to object
2. Export to .usd
3. Import back to max (looks correct)
4. Reference as usd stage (looks wrong)

**Expected behavior**
It should look the same.

**Attachments**
Tested material setups:

**Specs (if applicable):**
- 3ds Max 2026.3
- USD v0.13.0.7

Reproduce the workflow in 3ds Max 2026.3 with USD v0.13.0.7: export a material-bearing model to .usd, import it directly, then reference it as a USD stage. Compare the material results and trace the plugin's material handling for these two paths; done means the referenced stage matches the direct import.

Written by the indexing model from the issue text.