This is an Internet Explorer feature only.
The AutoDetectPasteFromWord function checks if the text you are trying to paste comes from Microsoft Word. If so the editor will launch the "Paste from Word" window so the user can paste inside of it, clean up the code before inserting it in the editor.
You may disable this option by setting it to 'false'. In this case the text will be pasted into the editing area directly.
FCKConfig.AutoDetectPasteFromWord = false ;