Oh man, I wish I knew. Have you noticed this one? You're editing a wrapped paragraph, you use the right-arrow key to move, and once you're at the end of -any- line, it suddenly jumps down to the "..." (the toggle for displaying the quoted message).
Ah, is that what's happening? All I know is I go back to proof my email before sending and I keep randomly ending up at the bottom and cursing as I scroll back.
(Also, why hide the formatting bar...)