Concurrent Vortex of Projection effects cause an anomalous number of hits/explosions

Two simultaneous Vortex of Projection triggers after firing 2 Frostbolts somehow causes 3 hits. Doing the same after firing 4 Frostbolts somehow causes 7 hits.

Demonstration (youtube)

Setup:
100% spell poison chance, Golden Rule, some cold gained as chaos so Vortex can poison, Brutality on Frostbolt so it can't. One Vortex gem in a Focus helmet, another in a trigger weapon, letting them trigger simultaneously due to different cooldowns.

Results:
- Simultaneously triggering two Vortex skills after firing 1 Frostbolt correctly causes one explosion from the Frostbolt, and one explosion from the player.

- Doing the same after firing 2 Frostbolts causes an explosion from each Frostbolt, but this somehow hits an enemy 3 times instead of 2.

- Doing the same after firing 4 Frostbolts causes 3 hits from the first 2 bolts, 2 hits from the 3rd Frostbolt, and 2 hits from the 4th Frostbolt, for a total of 7.

The initial cast/trigger of Vortex of Projection doesn't appear capable of exploding from a Frostbolt that's already targeted by another Vortex effect, but the 4 lingering explosions don't appear to have this restriction. This seems inconsistent/unintended. Even if it isn't a bug, it still doesn't explain the 3 hits from 2 frostbolts.

Bug report reference number 1.195.969.658

Two additional tests:

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Adding Return (in this case from Returning Projectiles Support) to Frostbolt prevents the additional hits for some reason, limiting explosions to 1 per Frostbolt. (A related bug report here.)

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Adding a third Vortex produces even more hits. What appears to happen is that Vortex 1 destroys Frostbolt 1 and deals 1 hit, Vortex 2 destroys Frostbolt 2 and deals 2 hits, Vortex 3 destroys Frostbolt 3 and deals 3 hits. Then Frostbolt 4 explodes, also dealing 3 hits. Total of 9 hits from 3 triggers with 4 Frostbolts.

What might be happening is, whenever any Vortex explodes from a Frostbolt, ongoing Vortex effects also explode from that Frostbolt? Is this actually intentional behaviour? (The Return interaction would still be strange in that case.)