I can reproduce this with the provided .xlsx, but not with
arbitrary LibreOffice .xlsx files.  The behavioral change is most
likely caused by the upgrade to 5.34[1].

[1] <http://git.php.net/?p=php-src.git;a=commit;h=d874d4a15c2e17a753d580691906c95e9153b823>

Just to add another note, I've hit this issue today with php 7.3.4
I've also tried resaving the xlsx with LibreOffice 6.1.5.2 (x64) and after that I get application/octet-stream as function return.

Encountered this issue a couple of days ago when trying an upgrade to PHP 7.4.0
With xlsx-files downloaded from Google Sheets.

Same problem with php 7.4.1 and a Word docx file (libmagic 537) - mime_content_type returns "application/vnd.openxmlformats-officedocument.wordprocessingml.documentapplication/vnd.openxmlformats-officedocument.wordprocessingml.document"

Worked well on old php 5.6.26 (libmagic 517)

Same problem with LibreOffice 6.0.7.3 and PHP 7.4.2.
Mimetype: application/vnd.openxmlformats-officedocument.spreadsheetml.sheetapplication/vnd.openxmlformats-officedocument.spreadsheetml.sheet

I'm experiencing the same issue in my Docker container with PHP version 7.3.11.

This also is affecting word documents.

Tested with:
- MAC OS 10.15.4/ PHP 7.3.4
- Ubuntu 16.04.6 LTS / PHP 7.3.13
- Ubuntu 16.04.6 LTS / PHP 7.3.14


$ file --mime-type test.docx
test.docx: application/vnd.openxmlformats-officedocument.wordprocessingml.document
$ php -a
Interactive shell

php > print mime_content_type('./test.docx');
application/vnd.openxmlformats-officedocument.wordprocessingml.documentapplication/vnd.openxmlformats-officedocument.wordprocessingml.document

I got the same issue with finfo(FILEINFO_MIME_TYPE, $file) in php 7.4.5 on linux

I am seeing this duplication with docx files downloaded from Google Docs.  When I open them in Word and do a "Save As", it works again.

Similar to what ryanmcquerry reported, if you open and save your xslx file in Excel, it also solves the problem. That's a good enough workaround for the time being, while the bug is not fixed.

I experience this issue with PHP 7.4.6 on Ubuntu 20 using docx format. I've tried opening and saving it from office365 but that did not solve it.

We encountered this problem on php 7.3.11, on FreeBSD 12.0, with some XLSX and DOCX files.
Is there an update or a workaround ? Or a scheduled patch maybe ?

Encountered this using PHP 7.4.19 both inside a docker container and 7.3 (don't have more specific info) on the Pantheon hosting platform. 

Confirmed that the mime type returned by

    $finfo     = finfo_open( FILEINFO_MIME_TYPE );
    $real_mime = finfo_file( $finfo, $file );

is `application/vnd.openxmlformats-officedocument.wordprocessingml.documentapplication/vnd.openxmlformats-officedocument.wordprocessingml.document` for a docx file that was exported from Google Drive. 

This problem did not occur with a docx file created in LibreOffice.

I got the same issue with PHP 8.0.3 and PHP 8.0.6 on Windows and Linux

This looks like an issue in libmagic?  Has it been reported
upstream[1], or has it been resolved there already?

[1] <https://bugs.astron.com/my_view_page.php>

I checked whether this bug still exists on the currently lowest-supported bugfix version, and it appears this is fixed. It must've been fixed between PHP 7.3 and PHP 8.2. Closing this now.