REST: actvityId seems to always be 'null'

Hello All.

Userguide has an example of GET /runtime/process-instances/{Id} call, which returns body with ‘activityId’ set to current activity:

   "tenantId": null

I have a VERY basic process (start->userTask->end) with 1 user task just started. Running GET /runtime/tasks?processInstanceId={myProcInstanceId} returns a ‘userTask’ task correctly. But GET /runtime/process-instances/{myProcInstanceId} always has ‘activityId’ nulled. I expected it will have ‘myUserTaskId’ (current activity) in it.

Am I missing something?