Commenting on a commit with @ does not send out a notification

When a comment on a pull request is created, a mail notification is sent to both the reviewer of the PR and the people mentioned with @ in the comment. That's fine.
But when a comment on a commit is created, there is of course no reviewer but even people mentioned with the @ do not get notified. This is preventing us from making effective code reviews.
As we cannot see why the commenting behaviour is different between a PR and a commit we consider this to be a bug rather than a feature.
(PS: Has this maybe already been fixed in a newer version?)