This is a relatively large molecule of 27 atoms. The Mopac7 dat file, below left, has been used, with either a AM1 or PM3 hamiltonian. The flat starting structure of 4'-Hydroxy-4-Azobenzenecarboxylate(-), the anion of a simple azodye with one hydroxyl group and a deprotonated carboxylgroup at the other end, is given in the top drawing. After optimization, which converged, the left products are formed: a non flat molecule, which has lost its carboxyl group as a CO2 molecule, one of the benzene rings reduced to a 5-ring and the azogroup forced into a 3-ring with the extraannular C-atom. The same starting structure gives a perfectly behaved optimized structure with Gaussian03W rhf/sto-3g (to mimic the meagre basis set of Mopac7), and in a Mopac type calculation under Gaussian with AM1, the correct result is obtained, too.
With the neutral molecule, the carboxyl-protonated species of 28 atoms, Mopac7 again is not able to produce a reasonable optimization result. This time the carboxyl group stays, but the azogroup is forced into a 4-ring with the nearest C-C edge, and the second benzene ring is pyramidally bound to one of the N atoms, see below right from Molden! G03W/PM3 or AM1 gives the correct structure, again.
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