If you have two switches connected via a trunk. The native VLAN on the trunk is VLAN 3. The two switches have a VLAN 2 and VLAN 4 configured on other ports (access ports). Now I am correct in thinking that VLAN hopping (via double tagging) is not possible in this scenario as none of the access ports on the switches are in the native VLAN on the trunk and therefore the original VLAN tag will not be removed to expose the secondary embeded tag.
I have this problem too.