Here is something you may or may not want to try.  Out of curiosity, it may or may not be useful, what happens if you write text at the top of the document, then use the pass next key through command and down arrow.  NVdA+f2.  What happens if you do this a number of times, then use read current line to see where you are.  Does taking NVDA out of the action stop the behavior?  While issuing this command before every down arrow in such a case is cumbersome, it may be useful.  I don't know if doing so is less work than what you did to work around the problem.

Gene

if I go back to the top and down arrow sometimes it puts me on the next line, sometimes it jumps to the bottom of the document. I did a google search for this issue and apparently others are having this issue with recent versions of office365. It was ok though, I just opened the file in google docs, finnished editing it then re-saved as a microsoft office file from google docs itself. Jaws works very good with the google office on the web browser.