Hi Xavier,
I'm using:
Windows10 home
Yahoo browser
The Forum screenshot:

When the banknotes were introduced, I went there by pure accident and it turned "read" in the colour. Then a couple of days ago it turned into "not read", which suited me fine!
Screenshot of "Numismatic questions"

Here you can see, a former message (before last line), where I made an answer, which is impossible, if I hadn't read the question first...... but it's marked with the unread colour?
Do you need more to analyze the case? Feel free to ask.
As it is now, the "Read" colour is used correctly again, so I'm not really bothered, but it shouldn't happen again.
Amicalement
Ole
Globetrotter
Coin varieties in French:
https://monnaiesetvarietes.numista.com