I am going to tell the story of fixing a very high priority bug that was 15 years old. Arguably the worst KIO bug.
In September 2011, against KDE 4.7, someone opened bug 281270: "When copying files to a removable disk, speed and progress reflect copying to the local cache not to the disk itself". The report notes the copy notification showed about 50 MB/s to a USB 1.1 device, which cannot go faster than 12 Mbit/s. The reporter had asked a kernel developer, Alan Stern, what was going on, and summed up his answer:
