@James *******
you're being told WRONG, an extension isn't cancelled automatically when your work permit is cancelled, YOU go cancel it yourself at the immigration office.
Stamping out on an 'open' extension doesn't cancel it either, nor does you stamping in on a free entry or a tourist visa OR even a new Non-B
When you go to get a new extension (especially based on employment) they'll see that you didn't cancel the extension correctly and you will be fined for it before they'll let you get a new Non-B visa or extension inside the country