Using the "Multiple Unit Train Control" mod. Paring 2 locomotives facing away from each other changes them to an MU variant, it does something to share/balance fuel and acceleration power so the backwards facing loco isn't dead weight.
Mining the electric train (in MU mode) gives this error
The mod Electric Trains (1.3.6) caused a non-recoverable error.
Please report this error to the mod author.
Error while running event ElectricTrains::on_player_mined_entity (ID 67)
ElectricTrains/control.lua:150: attempt to index field 'burnt_result' (a nil value)
stack traceback:
ElectricTrains/control.lua:150: in function <ElectricTrains/control.lua:147>