By default, FCK turns on the XHTML formatting option. Therefore, when some people use visual editing to change a complete HTML file, the Head part may be changed to look unnatural. The solution is as follows:
Open Include/fckeditor/fckconfig.js
Find
FCKCONFIG.ENABLEXHTML = TRUE; // Unupported: Do NOT CHANGE.
fckconfig.enablesourcexhtml = true; // unupported: do not change.
Change to
FCKConfig.EnableXHTML = false ; // Unsupported: Do not change.
FCKConfig.EnableSourceXHTML = false ; // Unsupported: Do not change.
Then delete your browser’s temporary file, refresh the current page, and you will find that you are no longer being pranked by FCK.