Yeah not really, nethashrate calculation is tad wacky, it's probably not calculated right.
One could say that it is wacky by design. The network hash rate displayed by the pools is not a point of time measurement of actual hash rate -- it is inferred from the difficulty of the most recent block. CryptoNote computes the difficulty target based on the solve times of the most recent 493 blocks from the last 24 hours.
When a significant amount of hash rate is getting added or removed, it is intentional that the block difficulty doesn't snap up to reflect it immediately... meaning it also won't show up immediately on the pools' Network Hash Rate estimate.