TYPO3 - 后端文件列表中未引用的链接文件

I have a problem with referenced files and images in the backend filelist. If i e.g. place an image on a page, this image is referenced in T3 BE filelist, so i can‘t delete this file in the filelist. Thats ok. But, if this image is linked to a local file maybe a .pdf or something, this pdf-file is not referenced in the filelist. So i can delete this file and there is no warning. It’s a 8.7. Installation. In T3 6.2 everything was ok. Anyone having an idea, how to fix this behaviour?

DB: sys_file_reference => FIELD:link = t3://file?uid=3

Screen BE filelist Screen content element