WP doesn't remove uploads from folder when removed from “Media Library”?

I’m wondering why WordPress doesn’t remove uploads from folder when removed from “Media Library”? I set limit to 5mb on WPMU but even if user removes everything from “Media Library” he can’t upload anything new because 5mb limit is still present.

How can I make WPMU remove user uploads when removed from Media Library?

Solutions Collecting From Web of "WP doesn't remove uploads from folder when removed from “Media Library”?"