pitch-segment-variant

I'm studying the pitch-segment-variant and noticing when the :segment argument includes a list, it doesn't seem to generate but the number of segments represented by the first digit in the list.

(setf bach (attribute-series '(leg 8)
                             '((s g2 d3 b3 a3 b3 d3 b3 d3) (g2 d3 b3 a3 b3 d3 b3 d3))))

(pitch-segment-variant
 bach :size '((20) (30) (40) (100)) :segment '(1 2)
 :position '? :variant '? :transpose '((0) (6)) :initial t)
=> ((s g2 leg d3 leg b3 leg a3 leg b3 leg d3 leg b3 leg d3) (s a3 leg b3 leg) (s g2 leg d3 leg b3 leg a3 leg b3 leg d3 leg b3 leg d3) (s f4 leg f4 leg))

However, when the :segment argument calls for the same number of segments, those are generated correctly:

(pitch-segment-variant
 bach :size '((20) (30) (40) (100)) :segment '(2)
 :position '? :variant '? :transpose '((0) (6)) :initial t)
=> ((s g2 leg d3 leg b3 leg a3 leg b3 leg d3 leg b3 leg d3) (s d3 leg b3 leg) (s b3 leg a3 leg) (s g2 leg d3 leg b3 leg a3 leg b3 leg d3 leg b3 leg d3) (s f4 leg f4 leg) (s gs3 leg f4 leg))

I expected the :segment '(1 2) [randomly] to alternate between 1 and 2 segments. Could anyone explain why that is not the case? Thank you!