/nodes/{nodeId}/lock REST API fails for content created by a deleted user

Description:

A user creates a document in the repository.  Subsequently that user is deleted.  When a second user calls the REST API to 'lock' the document, the call returns a success but the document is not locked.

 
Steps to reproduce:

 
1/. Install OOTB ACS v5.2.4.1
2/. Create 2 users ('leon' and 'josie')
3/. Logon on as 'josie' and create a site (josie-site)
 - add a folder
 - upload a document into the folder
4/. Invite user 'leon' to be a member of the site 'josie-site' as a collaborator
Using the REST API, check that both Josie and Leon can 'lock' and 'unlock' the document uploaded in step #3.
…../alfresco/api/default/public/alfresco/versions/1/nodes/{node id}/lock
5/. Delete user 'josie'
6/. As user 'leon', try to 'lock' the document created in step #3.
….../alfresco/api/default/public/alfresco/versions/1/nodes/{node id}/lock
 
Observed Behaviour

 
The REST API call returns successfully to indicate the document has ben locked, but when viewed thru SHARE the document is not locked.
            "cm:versionType": "MAJOR",
            "cm:versionLabel": "1.0",
            "cm:lockLifetime": "PERSISTENT"
 
Expected Behaviour

 
After a user has been deleted, it should still be possible to 'lock' content created by the deleted user.
 

NOTE: The same behaviour can be seen when using the /nodes/{nodeId}/content REST API