Doesn't happen all the time, but here's a sure-fire (so far) use case:

http://jira.atlassian.com

click 'Reported Issues'
click 'Edit' (not the jsessionid ??)
select 'JIRA' from the drop-down
select 'Any' in all dropdowns with that choice.
select 'View'

Now re-sort the rows by clicking any column header.