Quick Reply - strange behaviour

[KMxRetro]

Hi folks,
Just wonder if anyone else has come across this problem. I have the latest vB installed, and when using the AJAX-enabled Quick Reply feature, strange things are happening.

If I use the "click button to reply" version of Quick Reply, I post and it says that "This is a duplicate of a post you've made in the last five minutes" and redirects you to the thread. But it DOES post as it is supposed to.

If I use the "no click" Quick Reply, the user types the message in the QR box, clicks "Submit" and is brought to the flood protection screen - is shown a message that says he cannot post twice in 15 seconds, please wait 14 seconds. That page has the editor window on it, complete with their post. Again, the post HAS been posted correctly!

I've tried reverting to the default style/no plugins and checking the config.php for any unneccesary whitespace, and testing in other browsers. The option to turn off AJAX fixes it, but I don't really want to do that!

Any ideas, please?