Can't create a related user from Employee screen

Version: 7.0-20130110-001608

On a newly created database, with the Employee Directory (hr) module loaded:

Reproduction Recipe:

1) Go to Human Resources -> Employees -> Create
2) Complete the required field, 'Name'
3) From the 'Related User' drop-down, choose 'Create and Edit...'
4) In the 'Create: Related User' screen, complete the required field, 'Name', then click 'Save'

Expected Result:

1) A new user should be created
2) I should be returned to the 'Employees / New' screen, with the 'Related User' drop-down populated with the newly created user's name. This matches the behaviour of other components of ERP when a 'Create and Edit...' link is selected and the sub-form is completed successfully

Actual Result:

I get the following 'OpenERP Warning':

Invalid Action!

You may not create a user. To create new users, you should use the "Settings > Users" menu.

I can't think of a reason (constraints, etc.) why this behaviour differs between this use case and other form/sub-form cases.