json/users changePassword returns the wrong error message with multiple datastores

An attempt to change a password via json/users can show the error "Identity <user> of type user not found" when multiple datastores are configured.

Steps to reproduce:
1. Install OpenAM with embedded config store containing user 'demo'.
2. Configure a second datastore in the root realm. This datastore should not contain a 'demo' user.
3. Login as demo and try to change password through:

curl 'http://openam.example.com:8080/openam/json/users/demo?_action=changePassword' -H 'Content-Type: application/json'  -H 'Cookie:  iPlanetDirectoryPro=AQIC5wM2LY4SfcxEhnezSVV0EJXiKdZxjFV_k4fhwzQs8SQ.*AAJTSQACMDEAAlNLABQtOTE1NjYyNjU2NjI3MTQzMTY2MgACUzEAAA..*' --data-binary '{"username":"demo","currentpassword":"wrongpassword","userpassword":"changeit"}' 

or use http://openam.example.com:8080/openam/XUI/#profile/password
and when prompted for the current password, enter the wrong one.

Expected result:
HTTP 400:

Actual result:
HTTP 404:

Another case would be if an OpenDJ password policy was enabled which prevented re-use of old passwords. In this case:

Expected result:

Actual result:
HTTP 404: