I have a sneaking suspicion that was a rhetorical question...but since I asked myself the same question I had to answer it.
As I understand it, quite possibly incorrectly, double insulated means the machine provides safeguards such that it does not require a 3 prong plug and concurrently direct wiring to the 'ground'. As a result it relies on the neutral to search for a ground. Thus the safeguards are directional. When the wires are reversed at the receptacle, the directional safeguards within the machine are circumvented and where the case/frame/etc. would typically look for a ground through the 'neutral' were they to become charged, the case/frame/etc. Are constantly charged and when looking for a ground have only the 'hot' or positive wire and me.
Also of import.. As many times as I saw the word death in conducting (no pun intended) the search...I'm thinking I am fortunate all I got was a 'buzz.'