Surely if you don't press the Roll button, then the scope is still in "normal" mode whatever horizontal setting you set?
At settings of 100ms/div or slower the "Acquiring" message appears (it doesn't appear at 50ms/div), but surely that is just to let you know that a display will appear soon, as it will not appear on screen until it has travelled invisibly from right to left (for example, after 14 seconds with timebase set to 1s/div). Otherwise you might wonder why there's a blank display.
It seems to behave the same way as the faster timebase modes. The difference being that with the faster timebase modes, the signal travels so fast across the screen, that you don't notice the delay before it's shown on screen.
Roll mode shows the display rolling across the screen from right to left, as described in the manual. Calling the "normal" mode, "auto roll" mode as well, just seems confusing, as nothing is shown actually rolling. There's no mention of auto roll in the manual.