It's intentional. Silly, but intentional.
Try logging with Firefox.. in my experience FF doesn't lose the text you've already typed. I could be wrong - I haven't tested that out too much.
It does refresh with Firefox. It's annoying, but I've learned not to start typing until after the refresh, since I know it's coming.
I wonder, though. If I typed TFTC really fast, and hit the submit button, would the system accept the log???