I inspected an older home yesterday and need help writing up the main disconnect. The leg from the meter comes into the top and ties to the breaker. The lugs of the box go to a sub panel on the other end of the basement and the lead off the bottom breaker go to a sub panel in the kitchen.
The issue I see, if the upper main breaker is switched off, the lower breaker and the lugs to the sub will be disconnected, but the wires on the “outlet” side of the upper breaker will be live.
What I think that you’re describing is a back-fed main breaker which is fine as long as it has a mechanical fastener holding it in place. The fact that the lugs on the CB are still energized when the CB is in the open position is not an issue.