When I delete or change configuration of a l2tpv3 interface, it is not applied to the linux interface.
For instance, if I want to change l2tpv3 parameters, I have to
1. delete the interface (delete interface l2tpv3 l2tpethxx) then commit
2. delete interface at linux level (ip l2tp del tunnel tunnel_id xx)
3. Recreate the l2tpv3 interface with the new parameters.
Otherwhise the old linux l2tpv3 interface is left configured and the GUI is in an incorrect state (complain about the interface already exist...).