This text was taken from:
http://www.mindspring.com/~jonfoulke...wd_system.html
"Rear suspension - The rear suspension even provides passive rear-wheel steering as cornering forces increase. The rear wheels turn with the car and actually help steer for more stable tracking when cornering hard."
Though not a "bona fide" Subaru explanation, the "technique" is explained in text from:
http://www.advancedracing.com/grmart1.html
"By allowing a bit of compliance in the front lateral links of an A-arm type suspension, the rear axle will toe-in when the car enters a hard corner; on a straightaway where no cornering loads are present, the bushings remain undistorted and allow the toe to be set to an angle that enhances tire wear and stability characteristics. Such a design is a type of passive four-wheel steering system."