sounds like they ran the feeders to that breaker, somehow. If you are not comfortable troubleshooting something like this, I'd get a licensed electrician to check it out. Sounds like a potential dangerous situation depending on what is actually going on there.
Another possibility is that it's a sub panel, can you confirm that? It could be a sub and they just decided to feed it through a breaker instead of the main. Not sure if that is to code though and I see very little reason why to do it.
Could this be a new incomplete installation where an old service of perhaps 30 amps was back fed into one of the side breakers while awaiting a new service to be hooked up from the utility pole and connect to a new meter and then to the main breaker in that panel?
It was not unusual for old panels (with as little as two 15 amp fuses) to be mounted on the ceiling.
How old is the house?
How many breakers does the panel have?
Do you get coverage you can count on? From the bag of fertilizer? From your lawn sprinklers?