All vul, after E passed (!), I opened ONE NOTRUMP(15-17), partner TWO CLUBS, RHO now bid THREE DIAMONDS. I love to defend, but here it seemed right to bid in front of partner THREE HEARTS. To my surprise, partner RKCBs with FOUR NOTRUMP. FIVE DIAMONDS (1430) SIX HEARTS. 94.93% at matchpoints. well driven, partner.