Segments using tags stopped working

This used to work but recently it has stopped working for me. I have two tags, tag 1 shows 132 users, tag 2 shows 122 users but when i create a segment with tag 1 or tag 2 i only get 117 users. However, if i go in and create a campaign and select my main email list and then 'narrow by tag' and select the same two tags i get 190 users. Any idea what is going on?