I sent an Escort Cruiser with PD Ion Beams in one of it's slots off to take care of some pirate Destroyers that were blocking my expansion. The pirates launched their missiles, but the PD weapons didn't fire, either on the first turn when I was Defending and hadn't issued any orders and in subsequent turns, when I was very careful not to fire the PD weapons against the pirates. Am I missing something?

yup, they are definitely not firing, and they definitely should be. that's a bug. i have a suspicion of what's causing it as well.... should be a pretty straightforward fix. thanks for the report.

(should be patched as of r11970.)