Mention events are not displayed properly in email notifications

STEPS TO REPRODUCE

1. Login as Admin
2. Create an user (e.g .U1)
3. Go to a page and edit it in WYSIWYG mode
4. Type '@' to display the users mentions list
5. Select U1
6. Click 'Save & View'
7. Trigger the 'Notifications daily email' job (or the job corresponding to the user's set email frequency) from Scheduler.WebHome
8. Login with user U1
9. Check the email received

EXPECTED RESULTS

The mention event is displayed properly (like other events, from Pages for ex).

ACTUAL RESULTS

The event's name and body are displayed as strings:

mentions.application.name

respectively:

notifications.events.mentions.mention.description.by.1user