Suricata

In IPv4, UDP checksums can be 0, which means they are not used. I've come across such packets, and we consider them to have an invalid csum.

From http://www.ietf.org/rfc/rfc768.txt:

If the computed  checksum  is zero,  it is transmitted  as all ones (the
equivalent  in one's complement  arithmetic).   An all zero  transmitted
checksum  value means that the transmitter  generated  no checksum  (for
debugging or for higher level protocols that don't care).

It may be interesting to check that "csum would be 0, transmitted as 1's" case as well.

This doesn't (fully) apply to IPv6, as there UDP csums are mandatory.

Will provide pcap privately.