Username values not removed from User Picker and Multi User Picker fields after user is deleted in JIRA 4.1.1

Steps to replicate (in JIRA 4.1.1):

1. Create a new user (e.g. "a_tester")
2. Add that user to jira-users and jira-developers groups
3. Create a new issue (e.g. ABC-1)
4. Add the user to any User Picker field (e.g. "Owner" in my JIRA instance) AND Multi User Picker field (e.g. "Multiple Owners" in my JIRA instance) on that issue
5. Delete the user
6. Go back to view the issue, refresh the browser page (notice it does not show up anymore in the UI in either field)
7. Add a comment to the issue
8. Check the logs. You will see this error:
   2011-04-07 15:37:52,078 http-8090-4 WARN jthurmann 937x25029x1 xiu70j 172.18.240.108 /secure/EditIssue.jspa [issue.customfields.impl.AbstractSingleFieldType] Issue ABC-1 has an invalid value 'a_tester' stored in the field 'Owner'. User 'a_tester' was not found in the system.

Notice that the system doesn't complain about the Multi-User Picker field although the value is actually retained in both fields. It only complains about the User Picker field.

Now, go back and recreate the user:

1. Re-create user"a_tester"
2. Go back to view issue ABC-1. Notice that the user is back in both Owner and Multiple Owners fields

I believe this is a bug. If you delete a user from the JIRA userbase, the values should be deleted from all fields. It should only be retained in the history tables.

Morever, not removing it causes WARN statements in the logs during Full Indexing.

2011-04-07 14:41:10,375 IssueIndexer:thread-10 INFO jthurmann 840x59x1 xiu70j 172.18.240.108 /secure/admin/jira/IndexReIndex.jspa [action.admin.index.IndexAdminImpl] Re-indexing is 62% complete. Current index: Issue
2011-04-07 14:41:13,078 IssueIndexer:thread-3 WARN jthurmann 840x59x1 xiu70j 172.18.240.108 /secure/admin/jira/IndexReIndex.jspa [issue.customfields.impl.AbstractSingleFieldType] Issue VIDESC-5730 has an invalid value 'miglesias' stored in the field 'SR Owner'. User 'miglesias' was not found in the system.
2011-04-07 14:41:13,250 IssueIndexer:thread-4 WARN jthurmann 840x59x1 xiu70j 172.18.240.108 /secure/admin/jira/IndexReIndex.jspa [issue.customfields.impl.AbstractSingleFieldType] Issue TVSE-464 has an invalid value 'miglesias' stored in the field 'SR Owner'. User 'miglesias' was not found in the system.