I don't get your answer I think...
Do you mean the following:
When you have the following thing configured on the ex4200. It won't route that traffic when you have soft-version 10.3???
Set interfaces vlan unit 100 family inet address 192.168.0.1/24
Set interfaces vlan unit 200 family inet address 192.168.1.1/24
Set vlans test vlan-id 100
set vlans test interface ge-0/0/0
Set vlans test1 vlan-id 200
set vlans test interface ge-0/0/1