A scarily plausible one is that this was a dry run, to test responses throughout the region to an airliner behaving in an atypical fashion.
There also exists the possibility that someone is trying to get someone else to show their hand by revealing technical means that can locate the plane.
Those two points have a touch too much of the conspirator about them to me.

Particularly the 'dry run' suggestion; surely after MH370, regulations re transponders / ability to track a plane are bound to tighten up considerably making any follow-up considerably more challenging. Anyway, how do 'top' something like MH370? It's up there with Jack the Ripper, Lord Lucan & JFK for ongoing theories & conjecture; up until something's found to resolve the quesions at any rate.