Vortex of Projection makes Frostbolts Return; Frostbolts that Return this way can't be exploded

- Cast Frostbolt (supported by Returning Projectiles)
- Cast Vortex of Projection on it, which causes it to Return
- Additional casts of Vortex of Projection / Frost Nova of Frostbolts can no longer use the returning Frostbolt.

I don't know if the bug is Returning or becoming unusable, but one of those seems unintended.

Demonstration (youtube)