The new setting to change the unread marks to plain red text, changes the text to red but still bold instead of plain.
Subject: Unread mail in 8.5.1 - bold/red unread text
Same issue here. When you change to the plain/red option the text does start off red and non-bold, but if you click on another folder in your mail, the unread items change to bold/red instead of plain/red. At least that is how our users (and me) are experiencing it.
Red/bold is better than black/bold, but red/plain (as it was intended to be) would be best. Lotus should just offer all three options, actually.