We didn't 'change or alter a successful and proven feature'.
HTML editors in general cause problems when you copy from MS Word and paste it in to the HTML editor. The reason for this is that MS-Word generates non-displayed Microsoft specific formatting characters that conflict our HTML/text editor (or most anyone else's. Just try pasting text created in MS-Word into Google's Blogger text editor and see what happens. Hint: Google's editor gets confused by the Word control characters in a manner very really similar to what happens when you paste text created in MS-Word into our editor.)
If you are going to create text in Word, you should first save it out as a .TXT (text) file, then open that file in Notepad and then copy into our editor. That will strip out all the offending Word-specific formatting that messes up the HTML editor.
Our editor is not broke. Don't paste text from Word into it and it will work much better.