It seems invisible ZERO WIDTH SPACE (U+200B) characters are sometime inserted into comments. Specifically, in this comment, the first "/org/gnome/desktop..." string contains invisible characters, which I thought had been accidentally inserted by the user's text editor.
So I've copied the string in my editor, fixed it, and copied the result back into another comment. Strangely enough, the comment also had the invisible characters. Just to be confirm I didn't accidentally put back the previous string, I've checked it again, checked that it worked in my terminal, edited my comment and pasted that string again, but it still doesn't work.
This is how the last characters look before and after I paste it as a comment:
Am I missing something or does the comment system in some conditions creates these invalid strings?