Either that ATC transcript has lost something in translation or something definitely is wrong in the cockpit. On all exchanges between MH370 and ATC there are the readbacks by MH370 (which is as it should be) right until the last readback which is just a casual "All right, good night".
That last sentence simply doesn't match the previously professional responses. I know that ATC & pilot exchanges can be a bit casual at times but there's always (at least in the UK) a proper readback.
Any pilots still reading this thread wish to comment?