Hi,
Did you receive an answer to this yet? In case you did not, what you are seeing is the pretty printer reducing the first _expression_ to a shorter sequence representation.
The term "<<1, 1>>", which is a sequence, is the set of mappings 1 to 1 and 2 to 1, which is equivalent to "(1:>1 @@ 2:>1)". In this case, the pretty printer realizes that the left-hand sides of the mappings are the same as what they would be in a sequence and reduces the output to sequence form.
It think if you evaluated "{(1:>1 @@ 2:>1), (1:>1 @@ 2:>2), (1:>2 @@ 2:>1), (1:>2 @@ 2:>2)}" it would print the set of sequences you saw. (I don't have the toolbox handy to check myself, but I think it would do that.)
Hope my information is accurate and helps you,
Robert