Splicing Horobi's Whisper does not exile cards from graveyard until the spell is cast - two Whispers can exile the same cards

[Wizzerinus]

What is the expected behaviour of the card?

• Horobi's Whisper exiles cards from graveyard as the Splice cost is paid. Multiple Whispers spliced onto the same spell have to exile 8 cards from the graveyard.

What is the actual behaviour of the card?

• Horobi's Whisper exiles cards from graveyard as the spell is cast. The arcane caster can choose the same 4 cards for multiple Whispers being spliced on the same spell (which is incorrect).

Screenshot

Please provide a list of affected cards
Affects: [Horobi's Whisper]

Card Images