Gimbal lock

[DrAma999]

The problem you are experiencing with pitch is called Gimbal lock, it happens every time a rotation plane is parallel to another one. To avoid that you should use the attitude transformation matrix, or (better) the quaternion property.

[tropicdome]

Maybe a long shot, since it looks like this is not being maintained anymore, but I second this.

You easily notice the flip of the image when approaching e.g. 90 deg. (hold the device upright tilting back and forth will rapidly flip the image).

[tropicdome]

Also, your suggestion @DrAma999, may fix that the rotation axis is wrong when device is rotated into landscape.

[tropicdome]

I ended up using the answer from this thread on SO instead, it works great in both landscape and portrait mode
http://stackoverflow.com/questions/18972994/ios-7-parallax-effect-in-my-view-controller

// Set vertical effect
UIInterpolatingMotionEffect *verticalMotionEffect = 
  [[UIInterpolatingMotionEffect alloc] 
  initWithKeyPath:@"center.y"
             type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
verticalMotionEffect.minimumRelativeValue = @(-10);
verticalMotionEffect.maximumRelativeValue = @(10);

// Set horizontal effect 
UIInterpolatingMotionEffect *horizontalMotionEffect = 
  [[UIInterpolatingMotionEffect alloc] 
  initWithKeyPath:@"center.x"     
             type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
horizontalMotionEffect.minimumRelativeValue = @(-10);
horizontalMotionEffect.maximumRelativeValue = @(10);

// Create group to combine both
UIMotionEffectGroup *group = [UIMotionEffectGroup new];
group.motionEffects = @[horizontalMotionEffect, verticalMotionEffect];

// Add both effects to your view
[myBackgroundView addMotionEffect:group];