Whenever I killed an Elnoyle in the traditional method (Not using Blue Magic, ie: Degenerator) it stayed "alive" at the end of the battle. It's registered as defeated, yet the enemy model simply continues to float there. No idea why, and it caused me to wonder, but I guess I am not alone in this strange occurrence.

As for that of not recieving any items, try junctioning the Rare Items ability to one of your characters. Another thing that I have found to be odd is that if my characters use Mug on certain enemies, the enemy will not drop items. I noticed this to be true with Adamantiose, and it seemed to hold true with Elnoyle also.

I have no idea if what I mentioned there above is in fact true, but I definately seemed to be experiencing a pattern in how things were Mugged and then didn't drop those particular items.