[BUG] Shift + Enter submits the prompt instead of inserting a newline

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?

Sometimes <kbd>Shift</kbd>+<kbd>Enter</kbd> submits the prompt.

What Should Happen?

<kbd>Shift</kbd>+<kbd>Enter</kbd> should always insert a newline.

Error Messages/Logs

Steps to Reproduce

I can't find a way to reproduce it. It's unpredictable. The only thing I found was that restarting the conversation (terminate and do claude --continue) repaired the buggy behavior.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.9

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_