Under the heading "Is the tail the difference" the National Dog Magazine (Australia), October 1987, published an article on the difference between the Cardigan and Pembroke.
Regarding the temperament it reads:
Of all the differences between the two breeds, the difference in character is the one which is the least recognised by the judges. This is probably because it is not a physcial difference. Never the less it is a difference which affects the Cardigan to a large degree, especially in the show ring.
The Cardigan character is more placid and less excitable than that of the Pembroke. The Cardigan therefore does not usually display the same alertness or use its ears as well as the Pembroke. It is a characteristic which gives the Cardigan particular appeal to pet owners but which is often a handicap in the show ring."