Per-group IDM "REST-API Access" privilege assignment seems to be broken

Tried on 6.4.1.

Steps to reproduce:
1) Create a user with test_user_id
2) Create a group
3) Add user to that group
4) Assign privilege "Access the REST API" to that group
5) Make and IDM API call with test_user_id credentials. Tried it with GET http://localhost:8080/flowable-rest/idm-api/users/test_user_id
6) Error 403 Forbidden.

Assigning REST Access to test_user_id directly makes mentioned request work fine.