[Bug] Gmax Partner Eevee and Pikachu Revert to Base Forme after Max Mushrooms are Deactivated

[Snailman11]

Describe the bug

Deactivating Max Mushrooms on a Gmax Partner Eevee and Pikachu reverts them to their Base formes.

Link to Discord's Bug Report (GMaxing partner pikachu removes partner form after deactivating)
https://discord.com/channels/1125469663833370665/1305358886588649573

Reproduction

Deactivate max mushrooms on gmax partner eevee and pikachu

Expected behavior

Gmax Eevee and Pikachu should retain the form they were in before Gigantamaxing.

Screenshots / Videos

Gmax Eevee

Eeveelosespartner.1.1.mp4

Session export file

GmaxEeveeReverts.txt

GmaxPikachuReverts.txt

User data export file

No response

Additional context

Does not apply to Gmax Urshifu
https://discord.com/channels/1125469663833370665/1286367926525362176