Oh, We have this issue on imx53 before, The root cause is dhcp failure when you transfer to another port. So it still use the old IP. But the route is not right.
On our imx6's ICS version, we have solved this issue.
You can try two ways :
1. change init.rc like the following:
service dhcpcd_eth0 /system/bin/dhcpcd -AL
class late_start
disabled
oneshot
2. change framework code, when eht0 down, make clear IP action. I have attached my patch on imx6, you can refer to.
