Do you mean the "advanced options" of the media dialog? If so, could you give steps to reproduce?

I've just tested setting the location, type, border and size and all four worked well, and undid correctly with Ctrl+Z.

Sorry, I chose the wrong component, it should have been Wikieditor under Mediawiki Extension.

Steps to reproduce, I have tested this on IE, Chrome and Firefox,/

Go to page > Select Edit Source > Use advanced options to add a bullet list or somethings else like gallery etc. > Press Ctrl + z to remove it and it doesn't works.

Please provide a specific page where to reproduce this so I don't have to search or guess. :) Complete and full steps to reproduce are generally welcome, see https://www.mediawiki.org/wiki/How_to_report_a_bug for more info.

Sorry for that, let me give a user page for reproduction.
For e.g.
Go to my user page https://www.mediawiki.org/wiki/User:Apsdehal

Select Edit Source in top right corner > Use advanced options in WikiEditor to add a bullet list or something else like gallery etc. > Press Ctrl + z to remove it and it doesn't works.

Aha, right, yeah. Hmm.

Some browser support dispatchEvent + TextEvent
http://help.dottoro.com/ljuecqgv.php

var event = document.createEvent('TextEvent');
event.initTextEvent('textInput', true, true, null, text, 9, "en-US");
textarea.focus();
textarea[0].setSelectionRange(selection.start, selection.end);
textarea[0].dispatchEvent(event);

But all in all, it seems that this is one of those areas that is still a bit botched up in the browser landscape.