OK, more information as promised.
I got a mail with the virus, it was not deleted, but the virus was removed from the email. However, there was a second mail coming in at the time I was busy with the dialog asking me what to do.
When opening this second mail, the virus warning comes up again.
So it's not twice for the same mail, but for another mail. Apperently I do not get a warning for the second, only at opening.
(which is very fortunate !!)
Hope this helps.