Thanks Hannah for the explanation on 1 & 3. As for the bug, it has happened before. I think it usually occurs after zoom in and out or flip the canvas, it happens occasionally. In this example the rulers from other documents move around randomly with zoom and pan, and their appearance varies each time the canvas is moved or zoomed. Sometimes the whole rulers are visible like the screenshot, most of the time it's only part of the rulers in different sizes as they are cropped and scaled. It might be memory related, although Artrage was the only program running when it occured. I'll check on the memory usage the next time it occurs.