You are correct in saying that the management port is independent of the vr-default, but the condition you are experiencing is due to the fact the switch has a single mac address. The condition you are experiencing is not a L2 loop in the true sense but because you are connecting them to the same switch,with the same mac address, you then loose connectivity. In the true sense of "out of band", the two networks would never touch one another. Let me know if that is clear or you need more information.