mat2-cleaned .docx files are considered corrupt by Microsoft Word from Office 2010

I have a simple basic.docx file created by Libreoffice 1:6.1.1~rc1-2. I ran it through mat2 to get basic.cleaned.docx.

Using MS Word from Office 2010, i was able to open basic.docx without a problem. But opening basic.cleaned.docx shows this error message:

screencap

(the file open in the background of the screenshot is the original, basic.docx)

here's a text version of the error message, for searchability:

  Microsoft Word                                                      [?] [X]
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
The file basic.cleaned cannot be opened because there are problems with the
contents.

                                               [    OK    ] [  Details <<< ]
┌─ Details ──────────────────────────────────────────────────────────────────┐
│ The file is corrupt and cannot be opened.                                  │
└────────────────────────────────────────────────────────────────────────────┘

I'm able to open basic.cleaned.docx with LibreOffice 6.1.1~rc1 without a problem. I haven't tested any other .docx readers.

Edited by dkg