NEW YORK (TheStreet) -- Shares of The Macerich Company were gaining 8.1% to $75.53 Wednesday after rival mall operator Simon Property disclosed a stake in the REIT. Simon disclosed that it owns 5.71 million shares of Macerich, giving it a 3.6% stake in the company. Simon said it may ask Macerich to waive a provision that prevents it from owning more than 5% of the company.