4.2 double post and other AJAX(?) issues

[Snik]

I update 3.8.7 to 4.2.1 and having a big issue with quick reply option. Almost users are reporting that when they post using quick reply, after a few seconds they get a prompt that says "are you sure you want to leave this page?" with the option to leave this page or stay on this page. If they click stay on this page, it posts the message a second time (duplicate post).
Also, if user try to quick-edit post and press save button, edit window don't close (but after page refresh find changes saved).
Looks like problems with AJAX. Reproduced on all browsers. Any ideas?

[Paul M]

Almost certainly a Javascript error.
Do you have a mod installed that is loading custom javascript on your pages ?

You could use FF with firebug installed to see what JS errors are being generated.

[rughis]

I'm having the same problem :(

[ozzy47]

Follow the instructions in the post above yours. :)

[rughis]

General Options -> Disable Problematic AJAX Features :)

It seems I solved the problem :)