This is my experience.
When using Firefox:
Make a post using the QuickReply box.
FireFox returns the message: This page is asking you to confirm that you want to leave - data you have entered may not be saved.
The options are: Stay on page - or - Leave page.
Choosing "leave page" will refresh as usual, showing the new post - along with a duplicate post. The duplicate post seems to be hit and miss though, perhaps something to do with the timing between clicking reply and "leave page"?
Staying on the page allows me to try post again. If I wait over 30 seconds, clicking reply the post goes through without showing the "leaving the page" message box.
If I stay on the page and try post again immediately, the "leaving the page" message box pops up again. This can be repeated ad nauseam.
Internet explorer: same problem as in Firefox
Chrome: everything seems to work normally.