ImmersiveEngineering 0.12-83-403
Forge 1.12.2 - 14.23.4.2707
jei 1.12.2-4.9.2.196

This is a weird one..
if you broke a connector or relay that have a wire connection the wires just disappears and don't drop the coil as it suppose to do.. and if you tried to connect another wire on the remaining connectors, the message "You cannot attach this wire here" appears.
also if you are transferring power when this bug happens, you can put the connector again and they still getting power..
as probably my explanation isn't that good, i leave a gif of the bug: https://imgur.com/K7sjEVj
Sorry for the bad quality ;)