One of the most intriguing and defining features of the Tesla Model X crossover are the articulating falcon doors. These modified gullwing type doors allow easy access to the two rear rows of seats and are designed to sense closely parked cars as well as low roofs and can adjust automatically. Tesla Motors is reportedly suing Hoerbiger, which tesla contracted to develop the doors, didn't produce a satisfactory product, this then caused delays in the shipment of the Model X.
Hoerbiger was the early developer of the falcon door concept but their prototypes were faulty and leaked oil. Tesla farmed the work out to another contractor and it cost the company millions to move development elsewhere. Tesla's Model X is currently under production and the Falcon doors are supposedly working as expected.
Source: Autoblog