Done Trace triggers ability twice

[PrincessGardevoir]

What type of bug are you reporting? Mechanics

What is the bug?
Turn 9; when a Gardevoir switches into an Arbok, it Intimidates twice. This is caused by the game remembering that it needs to copy an ability with Trace, but is unable to copy Quark Drive, and holds onto needing to copy an ability. When Gardevoir switches in again later, the saved use of Trace activates to copy Intimidate, and activates, but the game then sees that the ability needs to be run again, and intimidates again.

Further note, this incident only occured because Trace also could not copy Comatose; If the ability were allowed to activate as normal (say, from sending out Jumpluff instead of Komala), then no bug occurs.

https://replay.pokemonshowdown.com/gen9randombattle-2456090983-vb5wqb0dv4uwgtaugmlqq7f5d71kolhpw

Are you able to replicate it? If so, how?
Yes, thanks to advice from JustOut459 in the Randbats room, who mentioned (then decided against) that it could be Quark Drive.


Confirmed replicated test:
https://replay.pokemonshowdown.com/gen9ou-2456096932

https://replay.pokemonshowdown.com/gen7ou-2456105076 Gen 7 replay of the same bug

https://replay.pokemonshowdown.com/gen4ou-2456106348 Gen 4 replay of the same bug
https://replay.pokemonshowdown.com/gen4ou-2456107403 Gen 4 replay of the same bug, but with Anticipation (that still activated twice!)

Confirmed non-activation of the bug tests:
https://replay.pokemonshowdown.com/gen9ou-2456099098 Having Trace activate on a Ceruledge switching into the initial Gardevoir being in avoids the bug triggering.

https://replay.pokemonshowdown.com/gen9ou-2456099623 Having the same as above, but that Stealth Rock wasn't also a triggering factor.

 

[Hydrametr0nice]

I think you're the first person to actually explain why this is happening haha. Thanks for the work you've put in! I'll look into it.
Edit: https://github.com/smogon/pokemon-showdown/pull/11488