documentManager not working in EL expression (workflow activation)

The following EL expression should work in a workflow activation filter, to restrict visibility of the workflow to users who have a specific permission e.g. 'MyPermission':

#{documentManager.hasPermission(currentDocument.ref,'MyPermission')}

However, the workflow does not appear for any users, whether they have 'MyPermission' or not. The following expression can be used as a workaround:

#{currentDocument.getCoreSession().hasPermission(currentDocument.ref,'MyPermission')}

or, if the opposite logic is required:

#{currentDocument.getCoreSession().hasPermission(currentDocument.ref,'MyPermission')==false}