In a job the Host group should be set by function :PUT_ATT HOST. The job fails with:
04.04.2017 14:24:41 - U00020916 Runtime error in object 'JAC#SCM.ALL.JCLLOAD_MBM8.UX.JOBS.COPYTEMP(1)', line '00001': Changing the Agent is not allowed because the resources of the agent has already been reserved.
It affects all kinds of jobs that have a
Host assigned. As
Host a
Host Group is assigned:
<Please see attached file for image>

In the preprocess of the job, PUT_ATT is used to assign one of the hosts from the host group as dedicated host:
<Please see attached file for image>

In
V11 this works no matter if
Generate at runtime is checked for the job or not.
In
V12, when
Generate at runtime is set, it fails with
04.04.2017 14:24:41 - U00020916 Runtime error in object 'JAC#SCM.ALL.JCLLOAD_MBM8.UX.JOBS.COPYTEMP(1)', line '00001': Changing the Agent is not allowed because the resources of the agent has already been reserved.