Packet distribution with NetworkConnection won't work

[g-a-s-o-]

In current(commit f2facc2) MSPSim,
NetworkConnection won't work properly.

I utilized an example program of Contiki-OS as follows;
Source code: /home/user/contiki/examples/ipv6/simple-udp-rpl/broadcast-example.c
And I created firmware for sky mote with following command,
make TARGET=sky broadcast-example

A mote executing this program sends 4 bytes of UDP message "Test"
to link-local allnodes multicast address with certain interval.
And, whenever the mote receives packets, it prints a message on USART1 Port Output.
I executed two MSPSims on a Instant Contiki 2.7 (Modified on 2013-11-15) which is running on VMware Fusion 6 Pro.
The command and option is as follows;
java -jar PATH_TO_MSPSIM/mspsim.jar PATH_TO_FIRMWARE/broadcast-example.sky -enableNetwork

In my understanding,
NetworkConnection encapsulates outgoing packets of CC2420 in TCP segments
and distributes the segments to other MSPSims through the loopback interface (e.g. lo).

I have captured packets on the loopback interface "lo" with Wireshark.
It shows that two MSPSims establishes TCP connection,
but no packet follows after this communication.

In addition,
I tried to distribute packets with using older MSPSims(commit 4b841fb).
Receiving packets are dropped in most cases
because RadioState of CC2420 is often being IDLE.
I guess this is not problem of NetworkConnection,
but motes with CC2420 rarely receives the distributed packets.

Please tell me if I use the wrong way.

Thanks.