Hi,
It often happens to me but there are two variations of it.
1, using "Post Reply" or "Quote" I get logged out and logging in again means nothing is lost.
2, Using "Quick Reply" I lost everything so often that I save all of it just in case with CTRL+A to select everything I've typed and the CTRL+C etc to copy and later on paste with CTRL+V. That's V for vomit, odd people programmers....
Regards, David