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Bug Report: Excel for Microsoft 365 Systematically Removes aca="false" Attribute from Formula Tags on Every Save — Causing File Corruption in .xlsm Workbooks

Maarten 0 Reputation points
2026-05-05T08:51:26.7633333+00:00

I am writing to formally report a reproducible and destructive bug in Microsoft Excel for Microsoft 365 (build rupBuild=27932, calcId=191029) that causes .xlsm workbooks to become corrupted after every save operation. The bug does NOT occur in earlier versions of Excel (pre-2021 builds).

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BUG SUMMARY

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Every time a .xlsm workbook is saved in Microsoft Excel 365, Excel systematically strips the aca="false" attribute from all formula tags (<f>) in all worksheet XML files. On the next open, Excel detects the missing attribute, treats the affected cells as invalid, and removes them — generating the following recovery log:

"Validation and repair were performed at file level. Certain parts of this workbook may have been restored or removed."

"Removed Records: Cell information from /xl/worksheets/sheet3.xml"

This results in permanent, silent data loss every time the file is saved and reopened.

Additionally, Excel adds a calcChain.xml file on every save, which it then flags as corrupt on the next open — further compounding the problem.

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REPRODUCTION STEPS

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  1. Open any .xlsm workbook with formula cells in sheet3.xml (the 3rd worksheet) that contain the aca="false" attribute on their <f> tags.
  2. Make any change (including simply opening and pressing Ctrl+S).
  3. Close and reopen the file.
  4. RESULT: Excel displays the "Removed Records: Cell information" recovery message. The affected cells are gone.

The problem is fully reproducible on every save. It does not occur when the same file is saved in LibreOffice Calc, which correctly preserves the aca="false" attribute.

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TECHNICAL DETAILS

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File examined: Energie_Analyse_Wind_v9_5_Dynamisch.xlsm

  • calcId: 191029
  • fileVersion: appName="xl" lastEdited="7" lowestEdited="7" rupBuild="27932"
  • Total formula cells affected: 4,768 across 35 worksheets
  • Formulas with aca="false" before save: 4,768
  • Formulas with aca="false" after save by Excel 365: 0 (all stripped)
  • calcChain.xml: absent before save; added by Excel 365 on every save

The aca ("Alternate Content Acknowledgement") attribute is part of the OOXML specification (ISO/IEC 29500) and its removal by Excel constitutes a violation of the file format standard.

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VERSION COMPARISON

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The bug does NOT occur in:

  • LibreOffice Calc 7.x (fully preserves aca="false" on save)
  • Excel 2019 and earlier (calcId < 191029)

The bug DOES occur in:

  • Microsoft Excel for Microsoft 365 (all current builds with calcId=191029)
  • Microsoft Excel 2021
  • Microsoft Excel 2024

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IMPACT

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This is a critical data-integrity bug. Users who save a workbook in good faith lose formula cells permanently on every subsequent open. The workbook degrades silently with each save cycle. For professional workbooks with hundreds of formula cells, this makes Excel for Microsoft 365 unfit for use with .xlsm files.

The current known workaround — manually re-injecting aca="false" into the raw XML after every save — is not acceptable for end users and should not be necessary.

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REQUESTED ACTION

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  1. Acknowledge this as a confirmed bug in Excel for Microsoft 365.
  2. Cease stripping the aca="false" attribute from <f> tags on save.
  3. Cease adding calcChain.xml to workbooks that did not previously contain it, or ensure its contents remain valid across save cycles.
  4. Issue a fix via the regular Microsoft 365 monthly update channel.
  5. Provide a status update on the Microsoft Tech Community and Feedback Portal.

I am prepared to supply the affected workbook file, the XML diff before and after save, and a step-by-step reproduction script upon request.

Microsoft 365 and Office | Excel | For business | Windows
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  1. Henry-N 12,630 Reputation points Microsoft External Staff Moderator
    2026-05-05T09:57:04.24+00:00

    Hi @Maarten, 

    Thank you for taking the time to provide such a detailed and well‑documented report. I understand your concern regarding the behavior you’re seeing in Microsoft Excel for Microsoft 365, where formula attributes appear to be removed during save operations, potentially leading to workbook corruption and data loss. 

    At this time, there has been no official announcement, service advisory, or confirmed fix published by Microsoft that specifically addresses this issue. As a forum moderator, I don’t have access to internal engineering logs, backend diagnostics, or product telemetry due to privacy and security restrictions. This limits my ability to validate or troubleshoot issues that may be related to Excel’s internal save or calculation engine behavior. 

    Because this appears to involve core product functionality and file‑format handling, any thorough investigation and resolution would need to be handled directly by the Microsoft product engineering team. 

    As forum moderators, I don’t have access to the detailed logs or backend systems needed to troubleshoot this effectively due to privacy and security constraints. The product team is in charge of the site, and they constantly check customer reviews and feedback, The higher votes, the more attention the related team will pay on. And a lot of features are developed and improved based on customer feedback.    

    How to Submit Your Suggestion to Microsoft.     

    Go to: Excel · Community then Send Feedback and Describe your proposal in detail User's image

    Describe your suggestion clearly for example:    

    “In Excel for Microsoft 365, saving .xlsm files strips the aca="false" attribute from <f> tags, causing formula loss and file corruption on reopen.” 

    After submitting your feedback, feel free to share the link here. I’d be happy to upvote it, and other users with the same need can support it as well. This also helps increase visibility across the Microsoft Q&A community.   

    Thank you for taking the time to share your experience. While this response may not provide an immediate fix, I hope it clarifies the situation and helps you move forward in the most effective way.  

    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread   

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