Question: Suppose I want to reduce risk of a circuit breaker malfunctioning and failing to disconnect a shorted circuit.

What if I install two identical breakers sequentially (one after another) so that if one of them fails the other one steps in and disconnects the circuit? Is there any problem with such installation?

Answer: 
Most generator manual transfer switch-over panels require you to do just this. The wire coming out of the breaker and going to a load (normally) is disconnected and channeled over to a second panel with another breaker and then then the biter-end coming out of the second panel is tied back to the load. In short, two breakers in series.
I have to agree: Connecting two circuit breakers of the same frame size and trip rating in series could be dangerous, depending on the application. When two circuit breakers of the same trip rating are connected in series it is impossible to predict which circuit breaker will trip first on a fault condition or on overload. The proper operation of the circuit breakers and clearing time would be affected. Connecting two circuit breakers of the same frame size and trip rating 
is simply not a good practice.