Finally found https://jira.atlassian.com/browse/JRA-33043

Problem is there is an "unassigned" user, probably created by an import.

The workaround that we managed to figure out was the following:
Create User A and User B
Turn off email notifications
Bulk assign all open unassigned tickets to User A
Bulk open all closed unassigned tickets and assign to User B
Delete the Unassigned user
Change all the tickets assigned to User A to blank value
Change all the tickets assigned to User B to blank value and close them
Turn on email notifications again

Still broken for us also.
JIRA v6.2.5 with JIRA Agile v6.3.13.1

We have the same problem here. When setting swimlanes by Assignee, "Unassigned" issues always show after assigned issues on the "Work" board.

Version 6.0.2
Build Number 6097
Build Date Tue Jun 11 00:00:00 CDT 2013
Build Revision e270beb0c7ea5a2c85312b90f01dbc0061802cf4
Installation Type Standalone
License Type JIRA 500 Users: Commercial License

Unassigned Issues Enabled true

JIRA Agile - 6.3.6.1
Plugin byAtlassian

Java Version 1.7.0_15
Java Vendor Oracle Corporation
JVM Version 1.7
JVM Vendor Oracle Corporation
JVM Implementation Version 23.7-b01
Java Runtime Java(TM) SE Runtime Environment
Java VM Java HotSpot(TM) 64-Bit Server VM
System Encoding Cp1252
Operating System Windows Server 2008 R2 6.1
OS Architecture amd64
Application Server Container Apache Tomcat/7.0.29
Database type mssql
Database version 11.00.3000
Database driver jTDS Type 4 JDBC Driver for MS SQL Server and Sybase 1.2.4

Hi jeff.shea,

Thanks for contacting us about this problem. To let you know, the resolution "Handled by support" means that we have moved this issue from jira.atlassian.com (for bug tracking) to support.atlassian.com (for support investigation into this problem).

I've now created a support issue for you also, you will receive an email about this shortly. We would like to know exactly how this is happening on your instance so that we can reproduce the problem. Unfortunately as it stands we are unable to reproduce the same problem, but if you could help us by sharing your configurations we may be able to get closer to seeing the cause of this issue.

Thanks for your help.

Michael
JIRA Support Team Lead

Can someone tell me what Handled By Support means for resolution? This still an open issue as of GH 6.1.3.1. I also think this is a major not minor issue. The rank you assign to an issue not being respected in the sprint backlog when using swim lanes is a serious problem. It also creates a mismatch between what you see in Plan view and Work view. This is broken, IMO.

Hi Rob,

I have created a JIRA support ticket for you at support.atlassian.com and you should receive an email shortly containing a direct link to the support ticket. Please refer to that support ticket for any future correspondence relating to this issue.

In the future, please raise support requests such as this by creating an issue in our support system, https://support.atlassian.com, not in http://jira.atlassian.com. Our support engineers respond to cases in https://support.atlassian.com and creating an issue ticket there will ensure that your problem gets addressed as quickly as possible. Also, https://support.atlassian.com is configured so that only Atlassian and you have access to the case and therefore it is a more appropriate location for us to gather any required system and/or configuration data from you.

Thank you,

Michael
Atlassian Support