Here's an excerpt from the "list-queues/simple" group of test suite:

  (define z2 (list-queue-append! x y))

  (test '(1 2 3 4 5) (list-queue-list z2))

  (test 1 (list-queue-front z))

  (test 5 (list-queue-back z))

  (list-queue-remove-front! y)

  (test '(5) (list-queue-list y))

  (list-queue-remove-back! y)

It uses y after calling (list-queue-append! x y).  But according to the srfi spec,

"It is an error to assume anything about the contents of the list-queues after the procedure returns. "

Probably the (define z2 ...) line should be changed to

  (define z2 (list-queue-append! x (list-queue-copy y)))