GFCI Breaker - not tripped = outlets work, turn light switch on breaker trips, lights work but outlets do not
If the lights stay on while the breaker is tripped, they must be getting power from another circuit. That means the electrician has mixed wiring between two different circuits. A GFCI breaker trips if there's any imbalance between the hot and neutral wires connected to it; if the lights are sharing the GFCI circuit's neutral wire while also drawing some power from a different circuit's hot, the breaker should definitely trip. The arcing you mention further reinforces that the wiring for the lights has used a hot from a different circuit while using the GFCI's neutral.

What you need to do now is figure out what the second circuit powering the lights is, figure out where it's tied in to the lights, and either disconnect it from the lights, or make sure the lights only use the neutral for that circuit.