BRUSSELS -- Europe's highest court bounced a chocolate-bunny case back to the Austrian Supreme Court with a ruling Thursday that still left open whether Chocoladefabriken Lindt & Sprüngli AG is entitled to a trademark for its foil-wrapped Easter treat.

An Austrian rival, Franz Hauswirth GmbH, had claimed the Swiss chocolate maker's trademark on the "Gold Bunny" should be cancelled, since Lindt acted in "bad faith" when it sought the mark in 2000. Lindt had previously sued Hauswirth, which sells its own gold-foil-wrapped...