Effect of the more electropositive reaction of the oxidant reduction on the metal deposition process inside a porous electrode (PE) for a direct-flow potentiostatic regime of electrolysis is studied with the aid of a mathematical model that was developed previously. It is shown that the marked worsening of dynamic indicators characterizing the process (decrease in the rate of deposition and final weight of metal, its localization in a narrow layer near the front end of PE) is caused not only by the worsening of potential distribution inside PE at the expense of the oxidant reduction reaction but also by anodic dissolution of the metal deposit in cathodically unprotected areas of PE. The effect various factors exert on the dynamics of the emergence and development of an anodic zone inside a cathodically polarized PE and possible ways to suppress it are considered.