What action must a train engineer take if an improper short stop occurs in MATC mode?

In the scenario where an improper short stop occurs while operating in MATC (Manual Automatic Train Control) mode, switching to MCS (Manual Control System) mode and platforming the train is the appropriate action. This procedure ensures that the train operates safely and efficiently after an unexpected stop, maintaining control over the situation.

By transitioning to MCS mode, the train engineer can manually control the train, which is crucial after any malfunction or irregularity in the automatic system. Platforming the train refers to aligning it properly at a platform while ensuring the safety of passengers and compliance with operational protocols. This action underscores the importance of taking a deliberate and controlled approach in response to any operational irregularities, thus prioritizing safety and proper train management.

Other options do not align with the necessary safety protocols. For example, notifying the conductor might be important, but it does not address the immediate need for control over the train. Stopping the train immediately may not be viable if the train is already stopped or in motion, and ignoring the signal directly contradicts safety procedures and could lead to hazardous conditions. Thus, switching to MCS mode while managing the situation is the most responsible and safe choice.