Just noticed this edit on my deleted message above:
"[edit Joerg: doubleclick on "send"]"

Let me assure you that that was not the case. I clicked "send" and TMO started acting like it usually does when you post something, but after a while (it felt like 5 minutes, but may have been just 2) it acted like it had given up and I ended up on the same message editing page. So I clicked "send" again, following which two copies of my post appeared.

You may say it's my fault, I sent the message twice. I would argue that a well designed forum software should not allow a thing like that happen.