"Current Assignee" Validator fails if user assigns issue to another user

Summary

The permission to transition issues is set to be for the Current Assignee but when attepting to reassign the issue to another assignee through the transition screen, the transition fails because it claims that "User 'xxx' doesn't have the 'Transition Issues' permission" despite still being the current assignee and the issue is not reassgined.

Environment

(Optional - If Applicable)

• JIRA 6.4.11

Steps to Reproduce

1. Start up a JIRA 6.4.11 instance
2. Create a test project
3. Modify the project's permission scheme so that the "Transition Issue" permission only applies for the Current Assignee.
4. Modify the project's workflow of the project so that the transitions in the workflow has the validator set to be "Only users with Transition Issues permission can execute this transition.".
5. Create a screeen that has the "Assignee" field.
6. Associate the screen in the previous step to the transitions in the workflow.

Expected Results

The transition succeeds and the assignee will be changed to a different user.

Actual Results

The transition fails with the message "User 'xxx' doesn't have the 'Transition Issues' permission" despite still being the current assignee for the issue.

Notes

1. The JIRA permission helper claims that the user has the permission to transition the issue.
2. The Transition will succeed if you do not try to assign to a different user.