Theyre official spec is 12k with solar.
It IS capable of 12k output, when solar is there to supply the remaining 3k that the inverter itself cannot.
I think this only applies when 3kw of AC coupled PV is connected though, not DC coupled PV. If it was DC coupled, then it is still relying on the inverter, which is limited to 9kw.
I agree its not right, and they probably know that, but they arent going to change it now, with who knows how many they have sold. Having said that, I have purchased one myself.