The left-side "local files" box hangs as it displays the files. When I click in the vertical scroll bar, it begins to display the next group of files, then it hangs. Once the scroll bar reaches the bottom, I can scroll up and down smoothly without it hanging. I also noticed that the CPU utilization jumps up quite a bit during the "hangs".
That's probably a different problem. What version of WinSCP are you using?