I tried the approach above. I'm keeping all changes made in grid,
pushUpdate-ing them back to dataSource once the page where they were
made is active, there's no problem. The problem occurs when I want to
batch-send them to server after user clicks Save button in toolbar.
Because "saveChanges" event happens later than "requestStart" event,
changes done on not-active pages are not attached to dataSource data before
the request starts and are send in another batch which is unpleasant. I did some
nasty "hacks" to make things going, but it's not really a nice solution.
I tried to block the first request using preventDefault() method, but without success.