Undertrained vocabulary tokens cause silent substitution in structured-output tasks (forensic writeup + token list)

#175
by glitch003 - opened

While evaluating the official weights for production data integrity, we found that a set of vocabulary tokens with near-zero embedding norms (min 0.001 against a vocabulary mean of 0.899) gets silently substituted or dropped in echo and extraction tasks. The output stays schema-valid, so downstream systems can't detect it. Examples: "Purtro" is echoed back as "cole", and an order ref of "Kinhted" is extracted as "order_id": "shelled". The failures are deterministic; the worst tokens fail 16 of 16 samples at temperature 0.7. The effect is strongest in the Chinese web-boilerplate tail of the vocabulary.

This class of issue was previously raised for Qwen3.6 (QwenLM/Qwen3.6#33). Full methodology, token lists, and a comparison against Qwen2.5, Mistral, Llama, and both Gemma generations: https://ingot.tools/reports/qwen3-8-27b-glitch-tokens?utm_source=huggingface&utm_medium=community&utm_campaign=qwen-report-2026-08&utm_content=preflight-2026-08-26

Disclosure: I work on the scanner that produced the report. Happy to share the reproduction harness.

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