Repost from phpbb.com forum ;)
For example - when I click notification and website scroll to last post it is positioned incorectly, usually at the very bottom.
I figured out that it could be connected with generating qr_form_placeholder when this small fixed editor is shown.
I'll be really glad if you could you check this :)
BTW
Same thing happens on your demo page (https://boardtools.ru/QuickReply) with a little help of browser developer tools ;) - so I assume it could be some problem with code.