To reproduce - Have a page view with two pages - one empty and one with a grid - put some cell in the grid in edit mode and cancel its validation in the CellValidating event - at this point you cannot change the current cell in the grid (which is desired) but you are able to switch to another page in the page view, thus its SelectedPageChanging event fires (which is not desired)
There is a similar, and more virulent bug in rowvalidating since it won't even enforce staying in the grid. Moving to another tab or control, however, continues to fire the event, causing a validation error (which we display a pop-up for). Sometimes, the e