Microsoft has acknowledged a peculiar issue with Word that can cause files to be deleted immediately after they are saved. Users of the word processor are being warned to avoid naming their files in a certain way to avoid data while the company investigates the problem.

While having to meet specific criteria when saving files is not unusual, using an illegal name would usually simply result in an error message and a prompt to choose a different name. With this bug, however, the file appears to be saved when in reality is has been deleted.

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There are two main tiggers for the file saving flaw which affects Word version 2409, one of which is include a hash symbol, #, in the filename. The other is the use of capitalized file extensions.

Microsoft explains the issue in a post on the Microsoft 365 support pages:

Users may encounter an issue in version 2409 where their file is deleted after save if the title contains a capitalized file extension (.DOCX, .RTF) or #. The issue occurs after making an edit to the file and saving when prompted after trying to close Word.

While it looks into the problem and develops a fix, Microsoft has a few suggestions:

For anyone who has lost files without realizing until now, there is the chance that a recoverable version no longer exists in the recycle bin. Microsoft has no advice for anyone finding themselves in this situation.