Username with # character breaks on "Assign to me" operation

I managed to reproduce this problem in JIRA v3.11. Here is the steps to reproduce:

1) Create a username with # character like #tester
2) Login as #tester user
3) On the view issue screen, clicked on the "Assign to me" link as shown in the attachment screenshot

It displayed the "assign issue" screen instead of assign the issue directly to the user with username #tester as shown in attachment screenshot.