So it may seem that by accepting the cue bid, A has undertaken the ultim without encouragement from his partner. That is quite enough to announce the ulti in any case. The possibility of a XXI-catch had already occured to A when he accepted the cue bid, so he intended the four kings as an encouragement for it. Most players keep on hoping for some sort of miracle when the XXI's destiny is already sealed. C could have made the vol t much more difficult by playing the XXI at trick 3, when he could see that it was certain to be caught.
Conventions also vary according as to what announcements are obligatory after cue bids.
G bor R v sz's view is that a cue bid and its acceptance create such interesting situations that the holder of the pag t should not be allowed to disrupt the process without accepting some consequences.