Arria V, Hard DDR3 controller, OCT-RZQ questions

Hi

I'm currently implementing 2 DDR3 hard controllers on my Arria GX A5. This occupies Banks 7B/C/D and 4B/C/D. Additionally I need to place an OCT_RZQ for each one, which additionally occupies banks 7A and 4A with two SSTL-15-Inputs. Banks I dearly require for 1.8V/2.5/3.3V.

Now I learn that SSTL-15-Inputs are powered by Vccpd (i.e. 2.5V). Why does Quartus II deny then to assign 2.5V pins to banks (7A and 4A) although I don't have any 1.5V-Outputs on those banks? How do I have to deal with that issue?

Thanks!