We theoretically discuss electronic transport via Majorana states in magnetic topological insulator-superconductor junctions with an asymmetric split of the applied bias voltage. We study normal-superconductor-normal (NSN) junctions made of narrow (wirelike) or wide (filmlike) magnetic topological insulator slabs with a central proximitized superconducting sector. The occurrence of charge-nonconserving Andreev processes entails a nonzero conductance related to an electric current flowing to ground from the proximitized sector of the NSN junction. We show that topologically protected Majorana modes require an antisymmetry of this conductance with respect to the point of equally split bias voltage across the junction.