The vertical resolution is 8 bits. It doesn't says all 256 values must fit on one screen.
As a parallel situation, it would be unfair to consider the time zoom feature as a bug, just because it doesn't fit all the samples in the same screen without scrolling, right?
I see this 8 divisions instead of 10 as a display limitation, not as a bug. Yes, it could have been better, with 10 divisions drawn on the screen, but it's not.
One more thing, only 8 horizontal divisions instead of 10 is nothing when compared with only half resolution on some voltage ranges (as in 7 bits instead of 8 bits). I remember there were certain voltage ranges where the values were all odd when read by SCPI, which led me to the conclusion that some voltage ranges were just simulated in software by a x2 multiplication, instead of using a real voltage divider in the analog path of the measured signal.