There is no mystery here. It is a perfectly normal situation. Furthermore, there is nothing in the NEC that would require any preventive or corrective measures. And no, I am not pulling your leg.
Here is the basic truth: When a fault takes place in the tenant?s space, a large amount of current will flow. That current has to pass through the main breaker, the tenant?s branch circuit breaker, and any feeder breakers that lie in between the two. All of those breakers will see the fault current, and every one of them is going to react to it. All of them will be given the command to trip by their internal electronic or electromechanical protective elements. Whichever one actually manages to get open first will terminate the event, by stopping the flow of fault current, so that the rest of the breakers in the line will remain closed. Having said all that, what would make you think that any specific breaker (i.e., the one in the tenant?s space) will win the race?
The way to resolve this situation is to adjust the trip setpoints of the main breaker and any feeder breakers that are adjustable. You want the breakers further upstream to wait a bit before tripping, so as to allow the breaker closest to the fault to trip first. This concept is called ?selective coordination.? We are required by the NEC to include selective coordination for breakers in emergency (NEC 700.27) or legally required standby (NEC 701.18) systems. We are not required to do the same thing for the normal power distribution systems in dwelling units. The building owner might prefer that this be done, but the NEC does not require it.