Once, and only once have I noticed attacking the same guy twice within the same day. It seems logical that if a player can be attacked then there is a chance he/she will be attacked... then if that player comes on line, makes his own attack, breaking a peace treaty (assuming there is one), and logs off again then he/she is available to be attacked again. bearing in mind medal count and game progress, there is a limited number of people who can attack you. I can't believe the chance of attacking any one person is more than attacking another and hence it makes sense that, through pure chance you can meet the same person twice in relatively quick succession.
After all, don't they say if you give enough monkeys enough type-writers you will eventually get the complete works of Shakespeare... through chance!?