Ha--this is great! From Fa. Steve's link:
This usage derived from the supposed fact that when kangaroos see a man for the first time they typically stop dead and eyeball him for five minutes, then suddenly turn and scoot. The practice of staring idiotically into space for long periods followed by a rash and inexplicable jump to conclusions was thought to closely resemble the behavior of a jury or judicial panel, hence kangaroo court.

musick, I first took your title to be a summons (heh) for Capital Kiwi.