Duplicated mention notification

Summary

User is mentioned twice in 2 similar emails when that user is assigned and mentioned in a transition

Steps to Reproduce

1. Create a Reviewer field as User Picker
2. Create a screen with that field
3. Set that screen as the transition screen for a transition
4. Add Post function to assign Assignee with the user in Reviewer field
5. Create an issue
6. Transition the issue in which the same user is set to Reviewer and mentioned in the comment area

Expected Results

The user is only mentioned once

Actual Results

The user is mentioned in 2 emails 

Workaround

There is no workaround to have only 1 email when we want to assign and mention at the same time