The OSB internal artifacts (for ex. data sources used by OSB) are protected by a role called "ALSBSystem". The users who belong to group "ALSBSystemGroup" have access to these artifacts.
Since operator group is a WLS group, it is not able to provide required access on ALSB resources. To use any user in "operator" role to shutdown an OSB domain,
please add this user to ALSBSystemGroup as well using WLS admin console under :
Security Realms >my realm >Users and Groups
Once added to this group you may be able to cleanly shutdown the server with this user.