I have a Windows 7 application that uses sendto to send UDP packets to a DSP.

Fairly often, the first packet or the first two packets being send out are duplicated. I have confirmed that for each pair of packets,
I am executing a single sento call.

WireShark shows them being sent out twice, the only differences being the header and UDP checksums:
26 14.006331000 192.168.0.4 192.168.0.10 UDP 62 Yes Source port: 9 Destination port: 9
27 14.006637000 192.168.0.4 192.168.0.10 UDP 62 Yes Source port: 9 Destination port: 9
28 14.011313000 192.168.0.4 192.168.0.10 UDP 94 Yes Source port: 9 Destination port: 9
29 14.011392000 192.168.0.4 192.168.0.10 UDP 94 Yes Source port: 9 Destination port: 9

The short time intervals between the original packet and its copy suggest that this is happening within Windows.

Any ideas what may be happening here?