Currently, if the balancer tries to move a chunk and fails because it is too large, it will then attempt to split that chunk. If the split fails for any reason we mark the chunk as jumbo. This means that things like transient network errors and the config servers not being available for writes can lead to chunks being marked as jumbo incorrectly. We should only mark the chunk as jumbo if the reason it failed to be split is that it is in fact jumbo.