I'm finding it hard not to think this was all the pilots undertaking, going by the timing of events.
- ACARS was disabled as the aircraft crossed the Malaysian east coast.
- Aircraft continued on until TOC, whereby their last radio transmission was received as they were handed off to Vietnam? ATC
- Transponder then is switched off
So how has ACARS been disabled and the crew are carrying on as normal until TOC ? Unless someone was in the equipment bay.