UDP packets blocks

Hi,
I have a problem on receiving UDP packets on a WildFiremod board with
MCF5282 micro.
I have a program like this:

INT32 udpCallback(......)
{
      // if packet is a command, do work
}

int main(void)
{
      tcpip_init(0);
     gUdp_socket = udp_getsocket(0,udpCallback,0);
     udp_open(gUdp_socket,port);
    while(1) tcp_tick();
}

My problem is that after a couple of time (about 3-4 minutes) that program
runs without receiving command packets, if I send it a packet, it doesn't
execute callback. Only after 3 or 4 received packets it executes callback
and process all packets received. Packets are not lost, because when program
"wakes-up", it process all packets in the same order that it has received
them.
I think that buffer queue hangs for an unknown cause, and then re-starts
work in the right mode when buffer has more packets.
What might happens?
Thank you, regards
Mauro