Diff is wrong in Bitbucket

This is a bug actually and appears as a question on https://answers.atlassian.com/questions/37536758/diff-between-two-branches.

Basically when I compare branches or a pull request between the two branches I see a diff that doesn't show on when doing the diff from the git command line. In addition to this, when I change the branches the diff looks exactly the same (not reversed as I would have expected).