The only other things I can think of is:

1) You're clicking on "preview post" which is next to "submit reply" when you're finished typing. I've done that and then wonder where my post is.

OR

2) When you click over to open another window you inadvertently close the window you had NT open in and that erases your post.

Not sure if either of these scenarios is correct but I can't think of anything else. Maybe someone who is more computer literate (like Jo!) can figure it out.