Currently, if an account doesn't exist locally, we fetch from mainnet when it's referenced in a request.
We take advantage of this for our resetAccount and streamAccount endpoints - we can delete an account locally to pull afresh from mainnet.
However, when an account is closed, it is deleted from our cache and is thus pulled from mainnet again. This is a confusing experience if you've just closed an account locally that exists on mainnet - the account continues to stick around because we pull from mainnet.