This was not totally consistent before, but I think it's taken a step backwards in 1.7b5.

ferdinand 29 Jan 2017:

Never noticed this before, but it is indeed very obvious now. Hit a fast moving ship and the effect stays on the place on screen where the ship was hit while the ship speeds on and leaves the explosion behind.

megas 29 Jan 2017:

They stuck in 1.7b4 and before, but they do not now in 1.7b5.

george moromisato 10 Feb 2017:

Fixed in 1.7 Beta 6. Thank you; definitely a regression.

nms 18 Feb 2017:

I think they're fixed in x-y coordinates now. They should be fixed in polar coordinates relative to the ship's facing.

nms 26 May 2017:

During yesterday's stream I checked some older versions, and it appears they've never moved with the ship as it rotates. It's just gotten more noticeable because the new effects are bigger and last longer, tending to leave them floating in space or deep inside the ship.

Presumably, hit effects are either excess energy radiating into space, or are added by your ship's UI to show what ships are being hit. Either way, it makes sense for them to be attached to the part of the ship that was hit.