You trigger the "regen under fire" on yourself, it thinks you're shooting yourself. It's a small thing but this makes external shield generators useless.
The target you hit does not get the "regen under fire" so that works.
How to reproduce:
- make a ship that has shield regen and capacity, put shield supply modules on it or use this blueprint:
- fire at another ship (you must else it doesn't work)
- notice how your shield regen/sec is lowered since it's acting like it is under fire