Shift lock button does not work on screen after upgrade IOS iPad 4.2?

Yesterday afternoon released the new version IOS 4.2 to iPad, iPod Touch and iPhone. This update brings new features and improvements over the previous version, but something strange is the change of functionality that Apple has given the screen lock button on the iPad.
And so, after IOS upgrade iPad 4.2 I have seen the lock screen button does not work for such action, becoming a sort of mute sound 100% complementary to the volume control progressive.
Is the function of blocking the display rotation was not helpful? In my case I have to say that if it was, because every time I changed position on the couch looked like the screen iPad began to turn in all directions, causing a considerable dizziness.
Now, it appears that Apple has been most useful function mute sound this button and, IOS 4.2, this function has been changed completely. Do you prefer the button to mute the sound or to lock the screen?