You should probably use mkvmerge with "--identify-for-mmg" instead of mkvinfo.
Here's a scenario where mkvinfo fails:
1) Take a MKV file (file.mkv) with attachments (fonts, for instance)
2) Check if the output of mkvinfo shows attachments (yes)
3) Add a font attachment to it using mkvpropedit
Code:
mkvpropedit "file.mkv" --attachment-name "arial.ttf" --attachment-mime-type "application/x-truetype-font" --add-attachment "C:\Windows\Fonts\arial.ttf"
4) Check if the output of mkvinfo shows attachments (no)