Hangul Jamo sequences that describe a Modern Hangul syllable not displaying correctly on Microsoft Word

[chom-kwoy]

Defect Report

Title

Unnormalized Hangul Jamo sequences that describe a Modern Hangul syllable not displaying correctly on Windows

Font

The latest NotoSansKR-Regular.otf.

Where the font came from, and when

Site: https://github.com/notofonts/noto-cjk/releases/download/Sans2.004/17_NotoSansKR.zip
Date: 2025-07-01

Font Version

2.004;hotconv 1.0.118;makeotfexe 2.5.65603

OS name and version

Windows 11 (10.0.26100 Build 26100)

Application name and version

Microsoft Word Version 2505 (Build 18827.20164 Click-to-run)

Issue

1. Steps to reproduce
   Copy & Paste the contents of the "Character data" section below into Microsoft Word, and set the font to Noto Sans KR.

2. Observed results
   The Unicode string <U+1100, U+1161, U+11AB> fails to render correctly; the jamos do not combine together, as shown in the "Screenshot - Microsoft Word" section below. Note that the strings that describe a non-modern syllable (<U+1100, U+11A2, U+11F6> and <U+1100, U+1161, U+11F6>) render perfectly.

3. Expected results
   The jamos should combine, as shown in the "Screenshot - LibreOffice Writer" section below.

4. Additional comments
   I did a bit of my own investigation; it seems like Harfbuzz normalizes the string before applying the GSUB transformations. However, it seems like the font shaper that Microsoft Word uses does not apply any normalization. I don't know what the "standard" behavior is, so it could be a bug on Microsoft's part; but in any case, I believe it is still an incorrect behavior that needs to be solved.

I'm aware of the other issue that prevents "LV + T" combinations (e.g. <U+AC00, U+11AB>) from rendering correctly on Windows. However, this is a separate issue that prevents "L + V + T" from rendering correctly, if it is a Modern Hangul syllable.

Character data

간 - U+AC04
간 - <U+AC00, U+11AB>
간 - <U+1100, U+1161, U+11AB>
ᄀᆢᇶ - <U+1100, U+11A2, U+11F6>
가ᇶ - <U+1100, U+1161, U+11F6>

Screenshot

Microsoft Word (incorrect rendering):

LibreOffice Writer (on Linux, correct rendering):