instabilities in the integration scheme, as it is known that results from numerical integrations may not agree with the predictions from the continuum KPZ [@KPZproblem]. The Cole-Hopf transform is a standard way to account numerically for the integration of bounded KPZ equations and, indeed, Langevin equations with MN are by far more stable than their interface-language KPZ-like counterparts [@MN2; @MN4]. Nevertheless, we have also found numerical problems when integrating (\[mnminus\]), either when the extra term is written in logarithmic form or averaging for smoothing the gradient. All numerical attempts are unstable nearby the absorbing state, owing to the presence of the extra singular term. We leave, therefore, the numerical integration of a continuous Langevin equation, representative of the MN2 class as an open, challenging problem.

Discussion
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We have characterized the MN2 universality class, or analogously its bounded KPZ counterpart, which, as commented above, accommodates different physical phenomena. We have studied it from, somehow deceptive mean-field and field theoretical approaches, as well as by numerical studies. None of the analytical methods provides a satisfactory description of the phase transition present in this class. On the other hand, Monte Carlo simulations of two different discrete interface models, argued to belong to 