When they use their copy technique on Android 19/Dr. Gero, they copy their "Ki Absorb" ability, and if they run out of Ki while on this copied form, they transform into their next forms (UI and Damaged Seven-Three) without gaining the new stats. They can go back to normal if they absorb enough Ki to transform, but if they copy anything else (except the androids) they maintain that "fake transformation" and aren't able to go back.

I just checked the code, and the simplest solution would be to deactivate the copy ability for the absorb ki power 😛