Different margins between buttons in tag list
The dropdown has an extra space - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16757#note_56553160
The dropdown style should be adjusted (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16757#note_56628581)
The extra space is happening because the button has displayed inline. This causes the whitespace in the code to add an extra space.