Sorry, BrowserUk, looks like I missed detailing a step in my reasoning: the list to array assignment seems to happen in one "go", so the contents on the LHS of the assignment would only be printed once, whereas coercing a list to a hash appears result in the LHS being updated for every element of the list, and the assignment propogating before it is complete resulting in too many values being printed/joined.

From my observataions it would seem that the following is being printed: for even numbers of pairs (4 elements, 8 element, 12 elements):

"1--1-1" x (elements/4)
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(ie the print is call twice, once for key 1 having value undef, once for key value 1 having value 1) and for odd numbers of pairs (2 elements, 6 elements, 10 elements etc):

"1-1" . "1--1-1" * floor(elements/4)
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(ie print once where key 1 has value 1, then proceed as previously).