Hello Mathias,
As you say, it's very strange.
No there's nothing special, I can see them "normally" in the Windows Explorer.
But this morning I, may be, found an explanation.
I just gone to this site:
https://resizeappicon.com/And generated pictures for mobile development.
As a result I downloaded (i received) a zip file from the website.
The problem appeared in MultiCommander just after I unzipped (with 7Zip) the resulting zip file into a folder.
I have attached a screenshot to this post, one with MultiCommander and the other one with Windows 10 explorer.
Bye,
Hervé