Than simply ask responsible Broadcomm developer. They are willing to help.
That is good advice, I will seek out the developer.
Monitoring the "wlan0" interface won't lead to any more information. That's why I asked for the monitor interface - it should give 802.11 traffic, too. Curious it doesn't give anything at all, though.
Yes that is what I figured. Was the dhcpdump useful at all? I am going to try adding logging to hostapd, I didn't know that was an option. Perhaps that will give me more useful information.