iPad context rotates towards original orientation when is scaled with pinch gesture

I'm trying to make a user friendly pdf reader. I've assigned a pinch gesture to scale the PDF document. When I change orientation to Landscape , it displays fine. When I start pinching - PDF page rotates towards the original orientation (like the emulator hasn't been rotated).

shouldAutorotateToInterfaceOrientation is set to YES

pinching gesture function. sender = ViewController

CGAffineTransform myTransformation = 
CGAffineTransformMakeScale(sender.scale, sender.scale);
sender.view.transform = myTransformation;'

How to开发者_运维百科 prevent this from happening?