It occures when I changed of ship. The first one have in slot 0 : Missile + Pulse + Explosive.
But the second ship was another ship with another set of weapons and so slot 0 was only core place.
But you see the core appear with some impossible "pulse + explosive" effects. Moving the core will remove the bugs.
I'll be able to reproduce this one another time by switching from a weaponed ship to a unarmed pod ship (core + power gen + thruster only). Here again the core displayed some impossible weapon effect.