On larger portfolios, it often goes back to the top of the page when I use the back arrow.
For example, if I add a lot to stock number 35 in a 50 stock portfolio, when I'm done it takes me back to the top of the portfolio instead of staying on stock 35. This is very annoying when working with stocks in the bottom half of a large portfolio.
B Norman commented
Also, page down in a large portfolio goes more than a full page, skipping several stocks.