Let's consider following scenario: User is scrolling through a list of sorted questions/answer (or whatever) and on the Nth page decides to change the "shot items per page param". Currently after clicking it the page count will be reset and user will have to start from the very beginning.
This seems to me counter-intuitive and not user friendly. I suppose that when user decides to see more or less items on page it is actually most likely no supposed that everything should be started from the very beginning. It's just that user want to see more items starting from this particular chunk of data, i.e. starting from the first item currently visible.
As you can see from tags, this is more then a feature request, I'm not insisting that this is an erroneus behaviour but still believe this is worth to be discussed.