Merging pull request marked it as merged but didn't pull in/merge any changes (BB-8466)

Someone forks one of my repo (https://bitbucket.org/leledumbo/linguc) and make some changes, he then create a pull request to merge his changes with mine. I approve and merge his request but I got "unable to merge" message. But then, the pull request is gone, in his account the status is also approved and merged, but the changes are not reflected in my repo.