Opening the dropdown for "Assign issue" duplicates the number of users in that list

Summary

If the user opens the Issue Creation dialog (and probably other dialogs/screens with an user selector) and opens the dropdown in 'Assign Issue' multiple times, every time the number of users is duplicated.

Steps to Reproduce

1. Create 15-20 users in JIRA 6.5-OD-07, ensure all of them are able to be assigned issues (you need enough users to cause the user list in the Assign Issue dialog to have to scroll).
2. Create a new JIRA issue.
3. Click Assign, then hit the dropdown arrow in the Assignee field.
4. Scroll down (using the keyboard or trackpad/mouse, it doesn't matter) to the bottom of the
   list
5. Close the dropdown
6. Repeat steps 3 to 5 a few times

Expected Result

The list of users is constant

Actual Results

Every time the user opens the dropdown, the lists of users contains more duplicated users.