You know, it's hard to tell. In my scenario, ionization is supposed to render PD weapons inoperable (scrambles their special targeting systems)
I don't think I've seen a rate change. It just appears that sometimes the PD decides to fire and sometimes it doesn't. Then again, I think I've seen ionization work as it should, but maybe this is combining with another problem.
Possibly related, is that sometimes ships seem to act as if they have "run away if out of ammo" flagged when they don't. And when they are running, they don't seem to fire. This seems to happen more often if the ship doesn't have powerful enough weaponry to defeat the player. (I didn't think Nova checked for stuff like that, but...)
I was attacking a ship that had light weapons, and it would not stay hostile (it would revert back to yellow instantly) and try to run. Which also meant that its PD would not fire. However, as soon as I gave it a missile launcher, it would then fight back - until it was out of missiles.