Timeout seems to be related to IE8. Short test in Firefox gave no loss of cursor. Currently using IE8 64 and am still getting timeouts and loss of cursor.
Workaround is to highlight the existing text and do a cut and paste back into the body of the message which restores the cursor and allows the continuation of the post.
Timing of the loss of cursor seems to be a variable. Sometime I can enter more text before it occurs than I can at other times.