You can add multiple @mentions to a task in a task list, but the second person does not get a notification in their workbox, and does not see this task in their task list.
Steps to Reproduce:
- Create a new page
- Add 3 tasks.
- One mentioning @user2
- One mentioning @user2 and @user1
- One mentioning @user1 and @user2
- Look at the workbox for user2
- User2 only sees two notifications
- User2 only sees two tasks assigned to them
- User2 should see all 3 notifications
- User3 should see 3 tasks assigned to them