Picked asset files in system folder not cleaned yet after backup?

After backup my iPad (iOS 15 beta.8) through Finder (or iTunes on Windows), I could browse the backup folder using tools like 'iMazing'.

And I found there are remaining asset files in this folder 「AppDomainGroup-group.com.apple.mobileslideshow.PhotosFileProvider\File Provider Storage\photospicker」which are picked by PHPickerViewController.

I wondered why they were not cleaned by system and how long they will be kept?

Thanks for your reading and looking forward the answers!

They are considered as cache files and will be automatically deleted if your device doesn’t have enough storage. Please file a bug report if you think they aren’t correctly deleted when needed. Thanks!

Picked asset files in system folder not cleaned yet after backup?
 
 
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