ATM Traceroute middle packet loss?

  Seems that every traceroute across an ATM link will result in the middle
packet being dropped. The ATM Switch nor the Router have any idea that it
is the second packet.. weird! Anyone have a clue to why that is?

Tracing the route to ns2
  1 44msec 44msec 44msec
  2 ( 44 msec * 44 msec

Tracing the route to
  1 16 msec * 16msec