somebody may have done you the "favor" of using LocTite RED on the fixed cup threads. This is sometimes done on RH-threaded Italian and French cups to really insure against them unscrewing in use...but it's overkill. If RED was used you will have to heat the cup up with a torch or heatgun to break the bond, it has to get pretty hot but not so you'd scorch the paint.
And as others say if you don't HAVE to remove it, don't. (but someday you might)