If you add the Options Stacked Chard and by Device to the View IM Device Multitrend Top, the shown Summary-Graph is not correkt.
If you use the Option by Components, it is.
Conclusio: Stacked Reports on Device LEvel are not usefull.
The Answer from Support was in June 2017:
We would be willing to evaluate options to improve this behavior. But if the customer wishes to change it, they would need to engage product management (Jason Normandin) through an Idea. We are still in the process of determining if there is a reasonable workaround possible through OpenAPI / ODATA querybuilder.