So I took a look at the "killCrewOnPowerCoreExplodedChance" variable, and it seemed reasonable. So I went and shot down another BShip, made a save with the Dropship enroute, and loaded the Battlescape up. To my surprise, it worked! And has worked a second time since.
The only change I made was the above one to the FTD mod. It is possible that I just had two outlier Power core explosions in a row? At any rate, I will carry on. If the problem reasserts itself, I will upload a relevant save.
Thanks again!
Chris