Every time I've tried killing the Ancient Phalanx enemy recently, they've just disappeared upon reaching 0 hp. They don't drop anything, and it doesn't count as a kill on the Tally Counter. All of the other enemies that got added to both granite and marble areas post-Skeletron die, drop items and coins as normal, and count towards the tally counter. As I hadn't played Terraria (or Tmodloader) for over a year prior to the update to 1.4.4, I can't say if this was happening prior to the update or not.