It does if there are multiple commits, but if there is only one commit, if will use the commit title instead. I often rename pull requests because submitters do a very bad job of naming their pull requests. When I then "squash and merge" it will instead choose the commit title, which is the original bad title, and I have to rename yet again. Would be nice if we could just copy in the pull request title when "Merge pull request" is clicked and you're in the confirm view.