It switches defense and special defense. The mistake was my fault, not Serebii's.
This is the text directly from the dump:
まか不思議な 空間を つくる。\ufffe5ターンのあいだ すべてのポケモンの\ufffe防御と 特防が 入れ替わる。
Apologies for the inconvenience, thanks for bringing it to my attention.
(Have informed Serebii, details...