Chances are 1 in 17,576 QSO's, all things assumed to be equal on a number of considerations.
The chances of this happening for the succeeding QSO are exactly the same since the two events are not dependent or connected. Same is true of flipping a coin.
Explaination: Three letters form the suffix, each has 26 possibilities. Thus, 26 x 26 x 26 = 17,576
Normal reaction: Pretty rare! Wow!