Before I start, I'm afraid I have to say I cannot reliably reproduce this, but it has happened to me twice today.
When replying to a post I press the button to confirm, the button disappears, replaced by the "Watch This Thread" button, however, the post is not submitted. The text box does not disappear, I can happily copy and paste my post into a new reply box.
The twice it has happened today, I have noticed that someone else has posted whilst I wrote my reply. Not sure if this is connected or not.
My User Agent string is: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.11 (KHTML, like Gecko) Chrome/20.0.1132.47 Safari/536.11
PS. Just a little bug-bear of mine and not really a complaint, but when you press home on a wrapped line it goes to the beginning of the text not the beginning of the line.
Eg. Let's say this sentence is a long sentence and is wrapping on THIS word meaning everything beyond it is on another line and I want to go and change the word "word". If I hit the HOME key, it will go all the way back to "Let's" instead of "word".