  A very exotic decay mode at the proton drip-line, $\beta$-delayed
$\gamma$-proton decay, has been observed in the $\beta$ decay of the $T_z$ = -2
nucleus $^{56}$Zn. Three $\gamma$-proton sequences have been observed following
the $\beta$ decay. The fragmentation of the IAS in $^{56}$Cu has also been
observed for the first time. The results were reported in a recent publication.
At the time of publication the authors were puzzled by the competition between
proton and $\gamma$ decays from the main component of the IAS. Here we outline
a possible explanation based on the nuclear structure properties of the three
nuclei involved, namely $^{56}$Zn, $^{56}$Cu and $^{55}$Ni, close to the doubly
magic nucleus $^{56}$Ni. From the fragmentation of the Fermi strength and the
excitation energy of the two populated 0$^{+}$ states we could deduce the
off-diagonal matrix element of the charge-dependent part of the Hamiltonian
responsible for the mixing. These results are compared with the decay of
$^{55}$Cu with one proton less than $^{56}$Zn. For completeness we summarise
the results already published.
