Zabbix user with read access can acknowledge

A user with role "Zabbix User" who have access to read a host, can also Acknowledge events.
This would normally be fine, but in the case of a non-logged in user - which is mapped to user Guest, it is not ok.
These acknowledges comes up as Anonymous.

Would it be possible to change so that non-autenticated users mapped to guest cannot do acknowledgements?