Description

Mathematics created using the LaTeX linear input mode and then converted to professional initially render correctly and are accessible. However, after saving, closing, and reopening the document the equations mutate and become problematic for correctness of notation and for accessibility.

Video demo

Video: Math in MS Word Mutating when Saved and then Reopened (4 minutes)

Steps to reproduce

• Open a new, blank document in Microsoft Word.
• Insert a new equation using the ribbon (Insert > Equation) or by pressing Alt + =.
• In the Equation Editor, ensure the input mode is set to LaTeX.
• Type the expression \sin{x}+\cos{x}=1 and then build it up into "Professional" format.
• Initial Observation: Note that sin and cos characters are rendered correctly as non-italicized mathematical functions. Using the Read Aloud feature at this point will correctly pronounce "sine" and "cosine."
• Save the document as a .docx file, close Microsoft Word completely, and then reopen the saved document.
• Observe the equation again: The sin and cos characters are now italicized. Using the Read Aloud feature will not correctly pronounce the function names.
• Convert the expression back into linear mode.
• Observe the equation again: The LaTeX is no longer valid for the desired expression.

Expected behavior

After saving a file containing Office Math expressions created using LaTeX and reopening it the equations such appear and function exactly as before saving (both in professional and linear modes).

Actual Behavior

The equations' are corrupted upon saving and reopening the document.

Impact

This bug significantly undermines the reliability of the Equation Editor for anyone using LaTeX syntax. It breaks both the visual representation, underlying encoding, and accessibility of the mathematics.

Environment

I have reproduced this issue both in Windows and on the Mac.

• Windows 11 Version 24H2 (Build 26100.6584)
  • Microsoft® Word for Microsoft 365 MSO (Version 2510 Build 16.0.19309.20000) 64-bit
• macOS Sequoia 15.7
  • Microsoft Word for Mac Version 16.101 (25091314)