[syslog-ng] spoof-source performance issues

I'm finding that with a destination of udp("10.x.x.x", port(514) spoof_source(yes)) about half of messages get lost when going from one syslog-ng host to another at a high message rate (> 3k/sec). This is on 3.1 OSE and the hosts are on the same subnet and switch, so there shouldn't be any network devices interfering. Has anyone else had this same issue? My hunch is that it's either a performance issue with the way the libnet (I'm using 1.1.2.1 on SuSE 10.2) API is implemented or it's an issue within the libnet API. Has anyone else noticed performance problems when using spoof_source?