I have a file with 1.5 million rows. Geany 1.27 on Lubuntu (Ubuntu Xenial 16.04.1 LTS). Scrolling down with the down arrow key stops at line 1,118,483. I can go further down with page down or the scroll bar and reposition the cursor there, but the down arrow key stops again after a few lines down. No such behaviour in SciTe. Arrow up key keeps working fine all the time. File stats (with wc): 1514885 (lines) 50686174 (chars).