Stygian Firestrom MTX doesn't fully work with transfigured version

Hi,

Just noticed a weird bug regarding a recent MTX I purchased.

After doing a quick test, it seems Firestorm of Pelting + Stygian MTX doesn't have the skull popping out of the ground. It does turn blue though, just missing that part.

After testing on regular Firestorm that does work as intended.

Hope that's a bug and not intened, was hoping for the skull bit to entertain me.

Thank you!