A class of \Deltas\ = 1 transition is analyzed in the D-s(+)-D+ and (B) over bar (0)(s)-(B) over bar (0) systems. Short distance Wilson coefficients are calculated within HQET. Novel features of the transitions are discussed. We find that these transitions are unobservable in the standard model. (C) 2002 Elsevier Science B.V. All rights reserved.