Looks to me like it is an effect of the camera being very close blocking light getting into the stone and threrfore and obscuring light return. This happens with diamonds too.
You can see it very minimally in the Asha closeup in VB's photo, although not nearly as pronounced.
I thought as much, but remember seeing that on another generic CZ once - not close-up - and wondered if it was something to do with cut.
I'm still hot!! Only now, it comes in flashes.