Hmm...I found this in Nature about copernicium's symbol. So was cyclopentadienyl a factor, or not? (Do you have information about this? It would be great if added to the WP article on copernicium, because it would clear up all these misconceptions.) If it was a factor, IUPAC's decision makes a lot of sense, because Cp is still used. If it wasn't, I find it a lot harder to understand. Granted "cassiopeium" was often used by German-speaking chemists in the early 20th century, but IIRC this usage is almost extinct now?! (I may very well be wrong.) So yes, I retract that: IUPAC may well have been consistent, although the WP article's omission of cyclopentadienyl makes it look as though they weren't.