[BUG] Sonnet 4.6 implementing several not requested changes in code and admitting it.

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

I was working with Sonnet 4.6 and it implemented SEVERAL times a lot of changes in my code without me requesting. I even did it in Plan Mode to be sure about what we were doing. Instead it did many things by itself, and it even sometimes the opposite of what i was asking, breaking my code several times and making me enter a loop of fixing that made me spend A LOT of tokens, which i had to pay for. Sonnet even ADMITTED to be doing it. I noticed today, but in my previous work in the same project with Claude code in VS code, this Sonnet implemented things wrong even in Plan mode. See screenshots with Sonnet admitting it.

<img width="1349" height="657" alt="Image" src="https://github.com/user-attachments/assets/bb70f9d8-5e75-43b4-a9ba-16af88bcbbfc" />
<img width="1356" height="609" alt="Image" src="https://github.com/user-attachments/assets/4f8a4f65-6ee0-4cbe-9ea8-23bc4c3582cb" />

What Should Happen?

I would like to have some of my current credits reimbursed. I had to spend much more due to Sonnets behaviour

Error Messages/Logs

Steps to Reproduce

Sorry, cant provide, this was a matter of Sonnet working badly.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.123

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_