HTML editors in general cause problems when you copy text from MS Word and directly 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. Or, As lookandbuyme suggests, you can create the text in Notepad to begin with and skip using MS Word.
Also, for the best experience with the editor, I strongly recommend that you check your Account Preferences Page and make sure that the checkbox for 'Use Design Editor v2.0 Beta' is checked. Editor Version 2.0 is really not Beta any more; we've had it on the site for several months and have been tardy in dropping the Beta designation. Version 2.0 fixes some known problems of the earlier editor version.