I think I saw someone communet that this bug only happens with the IPhone and not one iPad or iPod. Not so, I have an iPod 6th gen and it occurs on that too.
Extraneous feedback given to Braille users when navigating the Mail app
When using a braille display with the Mail app, after opening a message, at the beginning of each line of the email, the user will see who the message is from. This occurs in the header information as well as in the body of the message. When sorting by thread, each line also begins with the message number in the thread.