When a service is added, the package group is known. In the case of the order form, the client selects the Package within the Package Group. In the case with Staff, it's listed underneath the Package Group name in the package selection drop down. If you are changing it using re-assign pricing, any package of like module can be selected, regardless of Package Group. And the Package could belong to one or more package groups.
I think we need to add a second drop down menu after selecting the package / pricing to select the package group. I don't know if there is a need for using packages without being assigned to a group, since these cannot typically be ordered.
See attached screenshot. Reassign pricing has the package as the label. Adding a service has the Package Group as the label.. so when re-assigning pricing, we do not know what the package group should be.