PS: something else which will influence the Reverse List is the fact that if contacts didn't sign in for 135 days, they are actually removed from your list.
I dunno what 'removed' exactly means in this case, but I strongly suspect they are still visible as a list item in your contact list (which migh actually be a bug), but you will not recieve any updates/nick changes/etc anymore and you will probably notice that 'they don't have you' in the Contact List Cleanup. They aren't automatically added back; you must remove the contact and add it again yourself.
More about this can be found (somewhere) on
http://help.live.com/
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