Symmetry nonrestoration and inverse symmetry breaking on the lattice

We study the finite temperature symmetry behaviour of O(N1) × O(N2) scalar models on the lattice and we prove that at sufficiently high temperatures and in arbitrary dimensions their full symmetry is always restored or, equivalently, that the phenomenon of symmetry nonrestoration which, according to lowest order perturbation theory, takes place in the continuum version of these models, does not occur on the lattice.