Artwork: "Link the picture to this track" not saved

[Acoustics]

With MB 3.5b3

First, my artwork settings in the Preferences:




When I add an artwork to an album with these settings, the artwork is correctly embedded into the music files and correctly saved into the folder which contains the files. But in the Artwork tab in the file properties the checkbox "Link the picture to this music track" always remains unchecked, and only the Embedded artwork is available.

So the Album Artwork Manager detects that the files don't match the storage preferences too.

A link to an animated screenshot of the problem: https://we.tl/t-ZHjnLOkZGB

PS: this was working before. For albums added earlier, the two artworks (embedded and in the folder location) appear correctly in the Artwork tab. The problem is for new albums (or if I delete artworks of an existing album and try to add them again).
.

[Steven]

I am not able to reproduce the issue using the same steps in the video.
If any of the files already had artwork then MB would only update using the existing location properties for the artwork being replaced, so make sure each individual file really has no artwork already

[Acoustics]

I think I found the cause. I put an exclamation point ("!") in a folder name where the files are (not the brightest idea...), it seems it's what causes the issue.
I've reproduced the issue in another folder location:
OK with: C:\test\
NOK with: C:\test !\

Probably I'm going to remove the ! to avoid some other problems.