Hi guys, thanks for the responses.
To start off, it happens in all browsers that I've tested, IE8 + 9, Latest FF & Chrome on multiple machines. So I'm guessing it's not a browser issue.
1 . It doesn't happen every single time. About 80% in tests trying to edit the same page over and over.
I might be wrong, since the site was inherited, it's been upgraded from 4.2 (was working without problems) to 4.4 (so I'm not sure if the same version of jquery is used for example etc), but I don't think so.
Luckily, it's not a big issue for us so I'm actually going to let it rest now - the tiny inconvenience isn't really worth spending more time on for now, but thanks for the replies.