  The peculiar isospin properties of the b -> c cbar s current lead to a rich
set of isospin relations for the B -> Dbar(*) D(*) K decays which are presented
here. Recent high quality experimental data on the complete set of these decays
(22 measurements) are analysed in this context, the isospin relations are
tested and the results for the isospin amplitudes are discussed. The comparison
between the measured and expected branching fractions yields a new measurement
of the ratio of branching fractions Br(Upsilon(4S) -> B+ B-)/Br(Upsilon(4S) ->
B0 B0bar)}=0.86 +- 0.13. We finally discuss the implications of our findings
for the measurement of sin(2 beta) and cos(2 beta) using these decays.
