It seems like I can't select AdvancedHMI components and Power-Pack components at the same time, either by dragging a box around them, or using shift-click.
If the drag-selection includes one or more P-P components, only the P-P components get selected. If the drag-selection doesn't include a P-P component, then the AdvancedHMI components get selected.
If you select a P-P object first, then shift-click (or Ctrl-click) an AdvancedHMI object, the P-P object gets de-selected.
If you click to select an AdvancedHMI object first, then you can't select a P-P object at all with shift or ctrl-click.
There is obviously something that is making them "exclusive".