Sync doesn't decrase in size

I worked on https://tools.wmflabs.org/mix-n-match/?mode=sync&catalog=37. There are 4.5k connections on WD but not "here" and almost the same viceversa. I've tried those buttons but no significant changes. I've also cleaned all dups ("here" and on WD). Again those numbers still remains high. Is this a bug? Or there is something else to do (so a bug in documentation :P)?