While migrating from Extjs 4.1.3 to 4.2 we noticed that the store.pageMap.clear() no longer exists. We were using this to reset the PageMap to a clean state before loading the buffered store. This is demonstrated in this post http://www.sencha.com/forum/showthre...g-in-4.1/page3

Note our store is being filtered by server side code so we need to be able to "reload" the store based on this filter. Currently without being able to have the functionality of the pageMap.clear() we are unable to load the store without issues with the scrolling. Basically the scroll allows us to scroll to locations that do not contain data.