CLAUDE_CODE_NO_FLICKER=1 causes duplicated output and garbled Unicode on Windows

[Avimarzan]

Description

Setting CLAUDE_CODE_NO_FLICKER=1 in ~/.claude/settings.json env causes two rendering issues on Windows 11:

1. Duplicated output — the same text block (including tables, paragraphs) appears twice in a single response
2. Garbled Unicode — box-drawing characters render as mojibake when copy-pasting (e.g. ΓöÇΓöÇ instead of ───, Γö£ instead of ├)

Both issues disappear immediately when the env var is removed.

Steps to reproduce

1. Add "CLAUDE_CODE_NO_FLICKER": "1" to env in ~/.claude/settings.json
2. Start a new Claude Code session
3. Ask Claude to output a markdown table with Unicode box-drawing characters
4. Observe duplicated output and garbled characters when copying the response

Environment

• OS: Windows 11 Pro (10.0.26220)
• Shell: Git Bash
• Claude Code: CLI in terminal

[github-actions]

Found 3 possible duplicate issues:

1. [Bug] NO_FLICKER mode garbles Japanese text output on Windows #42406
2. New renderer (CLAUDE_CODE_NO_FLICKER=1): Japanese text clipboard copy garbled on Windows (UTF-8 → CP932 mojibake via OSC 52) #42417
3. [BUG] Korean text gets corrupted when copying (via /copy or selection) with new renderer enabled #42482

This issue will be automatically closed as a duplicate in 3 days.

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🤖 Generated with Claude Code

[Avimarzan]

This is not a full duplicate of the three suggested issues. Here's why:

Bug 1 — Duplicated output is completely unique to this issue. None of #42406, #42417, or #42482 mention text appearing twice in a single response. This is a distinct rendering bug.

Bug 2 — Garbled Unicode is related but not identical:

• [Bug] NO_FLICKER mode garbles Japanese text output on Windows #42406 and New renderer (CLAUDE_CODE_NO_FLICKER=1): Japanese text clipboard copy garbled on Windows (UTF-8 → CP932 mojibake via OSC 52) #42417 are Japanese-locale specific (UTF-8 → CP932/Shift-JIS)
• [BUG] Korean text gets corrupted when copying (via /copy or selection) with new renderer enabled #42482 is Korean-locale specific
• This issue affects box-drawing characters, which is a broader Unicode problem not tied to any specific CJK locale or codepage

All four issues share the same root cause area (NO_FLICKER renderer encoding on Windows), but this one covers a wider scope (non-CJK Unicode corruption) and reports an entirely separate bug (duplicated output) that the others don't.