jquery mobile going back to previous page becomes blank for seconds

From page1, ajax load page2, then change to page2, slide effect works fine.

$(":mobile-pagecontainer").pagecontainer("change",  "#page2", {transition : "slide"} );

From page2, ajax load page3, then change to page3, slide effect works fine. From page3, call $.mobile.back(); slide back to page2, works fine.

However from page2, call $.mobile.back(); the screen will become blank for about 1 or 2 seconds before going back to the page1. (there is no slide effect).

Any idea? thanks.