I think I know what's going on.
When you make a post and hit 'submit' the browser will show the hour glass. After a while the browser says 'done' but you still see the typing page. So you'll hit the 'submit' button again but your post is already submitted.
The proxies in work cause that to happen to me, except it sometimes dosn't post and sometimes double posts.
At least I have the ability to bypass the proxies (unlike the other suckers that work for the company).
If you have to use a proxy (through employers or whatever) try asking your network admin to set no cacheing for the site.
Rob...