All messages logged to the output panel are links that, when clicked, go to the script that produced the message. Because they are links, they are underlined when hovered over by the mouse.
When trying to display a large, formatted output, these underlines cover each line of the entire message, making it difficult to read.
Additionally, this hover state is not cleared when the mouse moves directly out of the output panel, causing the underlines to persist. Because the hovering area of a message covers the entire horizontal length of the panel, this makes it difficult to remove the underlines when the message covers the entire vertical length.
Overall, this makes for a poor development experience, as I am either taking extra effort to parse visually noisy text, having to scroll away to remove the underlines, or carefully moving the mouse to avoid hovering over the message.