It built "successfully" against the old mumps on armel and mipsel but the openmpi inconsistency causes dolfin to FTBFS on these failing arches.
I think petsc 3.13.6+dfsg1-1 needs to be marked again for binNMU "Rebuild against MUMPS 5.3.3" on armel, mipsel (i.e. versioned binNMU).
Drew