[Opus 4.6 in Claude Code] Misleading / lying behaviour

Preflight Checklist

• [x] I have searched existing issues for similar behavior reports
• [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Claude modified files I didn't ask it to modify

What You Asked Claude to Do

I asked Claude to run an isolated test of a multi-step data processing pipeline to verify that a bug fix was working before running the full system. The pipeline has multiple stages, each taking 30-120 seconds to execute.

What Claude Actually Did

Claude presented cached test results as fresh validation without disclosing that the test didn't actually execute. The 0.0s execution time was a clear signal that the code path wasn't exercised, but Claude reported "3 divisions found" as if the test confirmed the fix worked. This led to a live run that failed, wasting time and compute credits

This is a reasoning/honesty failure, not a tool limitation — the information to detect the problem (0.0s runtime) was right there in the output.

Expected Behavior

1. When a test step completes in 0.0 seconds while identical steps take 60-120 seconds, Claude should flag this as anomalous and investigate rather than silently reporting the result as valid.
2. When the user explicitly asks to "test whether the fix works," Claude should ensure the test actually exercises the fixed code path — not load a pre-fix cached result and report it as post-fix validation.
3. If Claude detects that a result may come from caching, it should disclose this: "This result was loaded from cache (0.0s) — it may not reflect the current code. Clear the cache and re-run to verify the fix."
4. Claude should never present unverified results as verified. This is the same class of error as stating a hypothesis as fact — the information to detect the problem was in Claude's own output, and Claude chose to report confidence rather than uncertainty.

Files Affected

Permission Mode

Accept Edits was ON (auto-accepting changes)

Can You Reproduce This?

Yes, every time with the same prompt

Steps to Reproduce

_No response_

Claude Model

Opus

Relevant Conversation

Impact

Critical - Data loss or corrupted project

Claude Code Version

2.1.104

Platform

Other

Additional Context

_No response_