Sorry I abandoned this thread! To anyone Googling for answers, this problem has shown up over a few generations of my application, and it’s always due to not properly managing the height of my containing divs. I imagine PM then gets an incorrect report of the height or visibility of the document, resulting in the aforementioned scroll behavior.
Sorry I don’t have anything more scientific; fixing it usually involves going through each parent container, making sure its actual height matches the visual height. More often than not, a containing div would be shooting off the end of the screen.