It indeed sounds like a bug, in the second case the switch will keep the miner's LAN interface alive so the miner expects to be receiving work from the pool, and whatnot, in the first scenario, however, the LAN interface will go to sleep mode, the miner knows that and thus "behave" normally, the firmware should check for internet connectivity and not LAN status.

On a side but related note, there should be an option on "What do to when your internet goes down", most custom firmware will keep the fans spinning while the hash boards shut down (the miner doesn't waste electricity), the stock firmware will keep on working for nothing (wasting electricity), it's easy to assume that the custom firmware way of dealing with it is better, but it isn't always the case, I have lost a few tens of miners because the internet went down on a cold wet day, and most of the miners that had custom firmware running died because the miner was colder than the room temp and the dewpoint was pretty low around the fan intake, water condensed and the miners rested in peace.

On the other hand, the gears that were on stock firmware were still generating enough heat and keeping the dewpoint at a higher level, and so they survived, to many people this whole relative humidity/dewpoint /temperature topic is irrelevant and they just want to reduce the power bill, to others, it's better to waste a few tens of dollars on miners that are burning electricity for no revenue rather than throwing away all of thier gears.