That certainly makes sense, but it doesn’t seem to happen quite the same way with other areas. For example, if you clear New Asagarth you can’t just walk down to the open field below and then walk back in and the city has completely reset itself. Likewise with the Summoning Place, you can’t clear out everything, step out into the desert and then walk back and everything has respawned.
With Sepermeru, you can effectively do this. You don’t even need to go as far as the Oasis. You can simply leave the western area of the city (through Westwall) into the desert there, walk back and everything has reset. So I guess I’m saying that it doesn’t seem to be tracking that the area that encompasses Sepermeru has been “in use” recently and should remain loaded.
I would completely expect this if, for example, you went to Sepermeru, then went north to the Highlands and returned back to the city. It shouldn’t work like this if you just take 10 steps out of the city. I believe requiring players to actively work to not cheapen their own gameplay, even inadvertently, is … suboptimal design, shall we say.