And at the other side of the resistor its 4.5V?
I would guess voltage divider effect.
Ex top output voltage if the lower 6 were set to inputs would be:
5V*(10K+10K+10K+10K+10K+10K+20K)/(20K + (10K+10K+10K+10K+10K+10K+20K)) = 5*80000/(1000000) = 0.4V, do the math on the others, add them up, and you will be under 5V.