From "http://tools.ietf.org/html/draft-ietf-6man-ipv6-atomic-fragments-00":
A host that receives an IPv6 packet which includes a Fragment
Header with the "Fragment Offset" equal to 0 and the "M" bit equal
to 0 MUST process such packet in isolation from any other packets/
fragments, even if such packets/fragments contain the same set
{IPV6 Source Address, IPv6 Destination Address, Fragment
Identification}. That is, the Fragment Header of "atomic
fragments" should be removed by the receiving host, and the
resulting packet should be processed as a non-fragmented IPv6
datagram. Additionally, any fragments already queued with the
same set {IPV6 Source Address, IPv6 Destination Address, Fragment
Identification} should not be discarded upon receipt of the
"colliding" IPv6 atomic fragment, since IPv6 atomic fragments do
not really interfere with "normal" fragmented traffic.
dd9082089d