DrRacket seems to suffer a lot from re-implementing typical GUI components. Scrolling a text pane is slow (unless there's a very small amount of text in it), clicking buttons sometimes produces no visual acknowledgement, the "close window" hotkey does not work on some windows (e.g., Preferences), etc. The most entertaining example I've seen was a few years ago when some users with Retina MacBooks were confused as to why the close/minimize/resize buttons in DrRacket were blurry while no other applications they ran had that issue.