Why does writeall behave strange?

I might overlook something here but I was wondering if you guys have an explaination for this behavior

So, what I did, I have some images in an imagedatastore. I selected within these imageset using a logical vector, followed by subset and writeall.

But I found that using 'FolderLayout','flatten' gives me logical results and 'FolderLayout','duplicate' gives me very odd results.

It changes the contents of the image compared to the file name, so a file would be labeled differently after using writeall.

Did someone else experience this behavior or is it me being situational?

Thanks in advance