Bazille bug? – Mapping Generator in increment mode -> Increment per voice instead per note – u-he Forum

It is deliberate because only this way can you stack voices and create modulation offsets between the voices. This way you can pan stacked voices differently, time them differently or otherwise let them do different things beyond simple tuning.

Related modulators such as random, stack index and alternate also deliberately create different values per stack voice.

Also, maybe it helps to take the perspective that voice stacking means “playing the same not so and so many times, at once”.