Right now if I am at the bottom (or top) of the text input for a cell, and press the down (respectively up) arrow key, Observable switches to the adjacent cell, pinning/unpinning cells as necessary, scrolling the page around, and committing/running the cell that was just left.
This violates the basic expectation of standard text boxes (on the web, in other apps, …) that the up/down arrows do nothing at the boundaries of the text. It is also disorienting, and the side effect of running the code from the cell that was just left can have unpleasant consequences. For example if some error was introduced, and many cells depend on that one, the page can end up scrolling wildly with the cursor off screen (I might have mentioned that elsewhere, but the page not re-scrolling in that case should probably also be considered a separate bug).
I don’t think it’s too much hardship for people to use option-shift-tab or option-tab for moving between cells. But if moving to the near boundary of the adjacent cell is important, a different shortcut like option-up/down could be used for this.