Cait Sith's Mewing Lullaby is not working as a light-based sleep

I noticed Cait Sith's mewing lullaby sleep effect is not working on enemies that it should be. It doesn't work in Vagary on the Dark/Earth hybrid elementals. Just to be sure, I went out to Xarcabard and tested it on low-level skeletons and dark elementals. They still resisted sleep.

Funny thing is, it DOES work on enemies that can be slept with dark-elemental sleep.
Cait Sith is a light-based avatar though, which is why I'm posting this in the bug section.

Surely this isn't intended, otherwise it doesn't make sense for Cait Sith to be light elemental.