in IE6 and IE7 is works fine, it strips out the formatting and pastes it in the editor as normal text.
in Chrome it copies the styles differently it seems,
The text on lipsum.com is formatted with only <p> elements around it, however when I copy a paragraph with Chrome it will add <span> elements around it, this is the <span> tag I get in the editor when I paste:
<span style="font-family: Arial; font-size: 11px; line-height: 14px;">
I think it's a chrome feature to make sure the formatting isn't lost when you copy some text, so it's not really a cuteditor bug but more of an anoying behavory of chrome which could be fixed by cuteditor ;)