If you have a CKEditor document set to fullPage: true, and place your cursor within the section of the HTML document, it will add extra HTML comments tags.
Example:
This has occurred for all versions of CKEditor. The test configuration of the editor includes these plugins:
about,a11yhelp,basicstyles,blockquote,clipboard,contextmenu,resize,toolbar,elementspath,enterkey,entities,filebrowser,floatingspace,format,horizontalrule,htmlwriter,wysiwygarea,image,indentlist,link,list,magicline,maximize,pastetext,pastefromword,removeformat,showborders,sourcearea,specialchar,scayt,stylescombo,tab,table,tabletools,undo,wsc,dialog,dialogui,fakeobjects,floatpanel,indent,listblock,menu,menubutton,popup,panel,richcombo,button,font,find,selectall,justify,colorbutton,showblocks,indentblock,colordialog,div,forms,iframe,iframedialog,autogrow,tableresize,stylesheetparser,bidi,dialogadvtab,panelbutton,print,docprops