I mutated Sawtusk Demolisher on top of a [[Striding Shotcaller]], then made two copies of the merged permanent. When I dealt combat damage to an opponent, all three of them prepared a spell, but only the original one prepared the correct 'Run the Play'. The copies prepared a Sawtusk Demolisher mutation instead.
Then when I tried clicking on the prepared Demolisher, then canceled the cast, it disappeared from exile. The second copy's prepared Demolisher remained, but it seems to be uncastable – nothing happens when I click it.
Forge Version: 2.0.12-SNAPSHOT-04.23
#My creature prepared a mutate spell. ._.
celest forge
tacit valeBOT
Creature — Troll Druid
Reach
Whenever one or more creatures you control deal combat damage to a player, this creature becomes prepared. (While it's prepared, you may cast a copy of its spell. Doing so unprepares it.)
0/4
Run the Play 
Sorcery
Put a +1/+1 counter on each of up to X target creatures. Those creatures gain flying until end of turn. Draw a card.
wraith tree
@crystal cargo maybe CardCopyService isn‘t the best for this? 🤔