LOL my perplexity, well used. I have three open most all the time, and try to go to my mail using only one of them. And read with another. I do a lot of searches, maybe that's how i lose some. When yours came in just then i looked at the board on purpose to see if it would disappear and they, your and Zorax's two, didn't, so it isn't that.
I still get notifications of messages when i shouldn't. The mail may be empty and 2-3-4 notifications come in, i go to mail and it's still empty. It's like it's catching up for messages that come in when i'm off-line. Or something.
Am not worrying about any of it any more.
It was Plato who said, “He, O men, is the wisest, who like Socrates, knows that his wisdom is in truth worth nothing”