- make IBSS connection between two devices
- send continuous broadcast PING from one machine

You can see, that there are multiple PING responses for each broadcast PING.
Sniffer reveals the reason:

One side retransmits PING reqs, because it receives no ACK for it. This is 
wrong. According to standard:

'Upon successful reception of a frame of a type that requires acknowledgment 
with the ToDS bit set, an AP shall generate an ACK frame. An ACK frame shall be 
transmitted by the destination STA that is not an AP, whenever it successfully 
receives a unicast frame of a type that requires acknowledgment, but not if it
receives a broadcast or multicast frame of such type.'

and:

'There is no MAC-level recovery on broadcast or multicast frames, except for 
those frames sent with the ToDS bit set.'

So, device must not retransmit broadcast/multicast frames since it must not 
wait for ACKs.
In the test above, retransmition of PING reqs stops upon reception of first 
PING reply.

Test was performed on two BG cards.