@"transform.rotation.y" animation loses layer opacity on an UIView subclass

I am using CAKeyframeAnimation for doing animations on a UIView subclass.

When I apply a transform.rotation.y (or transform.rotation.x), over a UIView subclass the object drawn loses opacity. I can't imagine why...

I test some scenarios:

• With transform.rotation.z, opacity is OK
• With position, opacity is OK
• Using a predefined UIVie开发者_如何学JAVAw declared at .nib opacity is OK with transform.rotation.y and transform.rotation.x

Is there any special consideration for transform.rotation.y and transform.rotation.x at -drawRect:?

Thanks for answers