Components are defined, Component Lead is a valid user with proper (Edit Issue) permission. And Component Default Assignee column is set to Component Lead.
After Editing the Component selection, the assignee of the issue remains unchanged. The Atlassian documentation appears to indicate the Issue Assignee would be updated.
I understand one way to get the issue assignee updated to Component Lead would be to use a workflow post function.
Jira 6.4.11