Shift in the underlining
Tyler edited a message, adding text not near the underlined text to see if it duplicates. @VictoriaDemierbe had underlined 'admiter' in red, and added a note to 'conduissons'. After Tyler added text at the beginning of the message, the underlines shifted. It's not merely a visual shift: if he selects any part of the word 'underline' after 'er', he is not able to add a comment or underline because it has a red underline, and he was able to add a comment to 'admiter' because it was no longer underlined.