I think I understand what you are asking, It sounds like the switch or the key is badly worn. The only time that the magneto's are checked is when you are on the ground, why be worried if the failure is on the ground? If the key does jam in the OFF position during a magneto check, simply let the engine come to a complete stop then restart after the key jamming problem is solved. (This will prevent engine and exhaust system damage) When the key is in the OFF position, the ignition switch grounds the magneto's. This prevents the magneto's from providing spark. When you check the magneto's, Left and Right on the switch grounds either the left or right magneto. This tells you that both magneto's are operational. Hopefully I am not insulting your intelligence but I do not know what you know about the ignition system. As I said before, YOU should notify the maintenance department and have them replace the switch. This only takes about an hour or less to replace and the piece of mind is priceless. As a student, you should not have to worry about this as you have enough on your plate just flying and navigating.
-Tom