Cannot batch remove preferred resources

Question
When selecting a workgroup on preferred resources all resources underneath are selected but when unchecking the workgroup resources stay checked?

Answer
This is by design:

When you select a workgroup to add on to your preferred resource list, the system is selecting everyone assigned to that workgroup at the time and add them to the preferred resource list. It does not actually add the workgroup on you list. You will notice even if you selected the workgroup initially, next time when you go back to the “Select Preferred Resources” dialog box, only the resources under the workgroup is selected, not the actual workgroup.