Case Roles: User/group assignments fail when using Case File

Case Management Showcase App is using Case File to insert user/group assignments when starting a case instance via kie-server-client API. The following method in particular:

String startCase(String containerId, String caseDefinitionId, CaseFile caseFile);

In this approach, there's a handful of scenarios in which user/group assignments fail when using Case File. The behavior slightly varies depending on the value of Adhoc autostart property for user tasks which had case roles assigned at design time.

These are the problematic scenarios:
Adhoc autostart = true
1. When a case role is assigned to Actors only in a case definition, case fails to start when groups are assigned to the case role
2 When a case role is assigned to Groups only in a case definition, case can be started when users are assigned to the case role, but when both users and groups are assigned - users assigned are ignored
3. When a case role is assigned to both, Actors and Groups (in different user tasks in a case definition), case fails to start when groups are assigned to the case role

Adhoc autostart = false
4. When a case role is assigned to Actors only in a case definition, case can be started when groups are assigned to the case role, but when both users and groups are assigned - users assigned are ignored
5. When a case role is assigned to Groups only in a case definition, case can be started when users are assigned to the case role, but when both users and groups are assigned - users assigned are ignored
6. When a case role is assigned to both, Actors and Groups (in different user tasks in a case definition), case can be started, but when both users and groups are assigned - users assigned are ignored

Point 3 is a critical bug, as it can't be fixed during case life cycle.
Points 4 and 6 are major bugs.
Points 2 and 5 are minor bugs.
Point 1 looks like the only proper behavior in terms of preventing users in entering data which can lead to errors during the case execution, but is inconsistent with other points and as such requires revision.